Digital VTR

ABSTRACT

In a digital VTR having a certain recording bit rate, within a range not higher than a remaining data rate after recording the bit stream, first HP data D 1  is recorded in first specific regions, and second HP data D 2  is recorded in second specific regions in specific tracks. In middle-speed and high-speed fast replay, the magnetic tape is transported continuously at a middle-speed or high-speed higher than the standard speed for normal replay, and the first HP data D 1  is used in common, and at a low-speed fast replay of about twice the normal speed, the speed of the magnetic tape is alternated between a speed near the standard speed for normal replay, and a speed near the low-speed fast, and at the speed near the standard speed, the second HP data disposed in the second specific regions in the specific tracks and the first HP data disposed in the first specific regions in the specific tracks are both replayed.

BACKGROUND OF THE INVENTION

The present invention relates to a digital video tape recorder (hereinafter referred to as digital VTR) having a track format for recordingdigital video and audio signals in predetermined areas on oblique track,and relates to a digital VTR in which the digital video and audiosignals are input in the form of a bit stream, and the bit stream ismagnetically recorded and replayed (played back).

FIG. 41 is a diagram showing a track pattern of a conventional, generalconsumer digital VTR. Referring to the drawing, a plurality of tracksare formed on a magnetic tape 310, in a head scanning direction inclinedto the tape transport direction, and digital video and audio signals arerecorded therein. Each track is divided into two areas, a video area 312for recording a digital video signal and an audio area 314 for recordinga digital audio signal.

Two methods are available for recording video and audio signals on avideo tape for such a consumer digital VTR. In one of the methods,analog video and audio signals are input, and recorded, using a videoand audio high-efficiency encoding means; this is called a basebandrecording method. In the other method, the bit stream having beendigitally transmitted; this method is called a transparent recordingmethod.

For the system of recording ATV (advanced television) signals, now underconsideration in the United States, the latter, transparent recordingmethod is suitable. This is because the ATV signal is digitallycompressed signals, and does not require a high-efficiency encodingmeans or a decoding means, and because there is no degradation in thepicture quality due to transmission.

The transparent recording system however is associated with a problem inthe picture quality in a special replay mode, such as a high-speedreplay mode, a still replay mode and a slow replay mode. In particular,when a rotary head scans the tape obliquely to record a bit stream,almost no image is replay at the time of high-speed replay, if notspecific measure is taken.

An improvement for the picture quality for the transparent recordingsystem recording the ATV signal is described in an article Yanagihara,et al, “A Recording Method of ATV data on a Consumer Digital VCR”, inInternational Workshop on HDTV, 93, Oct. 26 to 28, 1993, Ottawa, Canada,Proceedings, Vol. II. This proposal is now explained.

With one basic specification of a prototype consumer digital VTR, in theSD (standard definition) mode, when the recording rate of the digitalvideo signal is 25 Mbps, and the field frequency is 60 Hz, two rotaryheads are used for recording a digital video signal of one frame, beingdivided into video areas on 10 tracks. If the data rate of the ATVsignal is 17 to 18 Mbps, transparent recording of the ATV signal ispossible with the recording rate in this SD mode.

FIG. 42A and FIG. 42B show tracks formed in a magnetic tape using aconventional digital VTR. FIG. 42A is a diagram showing scanning tracesof the rotary heads during normal replay. FIG. 42B shows scanning tracesof the rotary heads during high-speed replay. In the example underconsideration, the rotary heads are provided in opposition, 180° spacedapart on a rotary drum, and the magnetic tape is wrapped around over180°. In the drawing, adjacent tracks on the tape 310 are scanned by tworotary heads A and B having different azimuth angles, alternately andobliquely, to record digital data. In normal replay, the transport speedof the tape 310 is identical to that during recording, so that the headstrace along the recorded tracks. During high-speed replay, the tapespeed is different, so that the heads A and B traces the magnetic tape310 crossing several tracks. The arrow in FIG. 42B indicates a scanningtrace by a head A at the time of five-time high-speed feeding. The widthof arrow represents the width of the region read by the head. Fractionsof digital data recorded on tracks having an identical azimuth angle arereplayed from regions meshed in the drawings, within five tracks on themagnetic tape 310.

The bit stream of the ATV signal is according to the standard of theMPEG2. In this bit stream according to the MPEG2, only the intra-frameor intra-field encoded data of the video signal, i.e., the data of intraencoded block (intra encoded block) alone can be decoded independently,without reference to data of other frame or field. Where the bit streamis recorded in turn on the respective tracks, the recorded data arereplayed intermittently from the tracks during fast replay, and theimage must be reconstructed from only the intra-encoded blocks containedin the replay data. Accordingly, the video area updated on the screen isnot continuous, and only the fractions of data of intra coded block arereplayed, and may be scattered over the screen. The bit stream isvariable-length encoded, so that it is not ensured that all the replaydata over the screen is periodically updated, and the replay data ofcertain parts of the vide area may not be updated for a long time. As aresult, this type of bit stream recording system does not provide asufficient picture quality during fast replay in order to be accepted asa recording method for a consumer digital VTR.

FIG. 43 is a block configuration diagram showing an example of recordingsystem in a conventional digital VTR. Referring to the drawing,reference numeral 1 denotes an input terminal for the bit stream, 2denotes an HP data format circuit, and 3 denotes a recording formatcircuit. Reference numeral 4 denotes a variable-length decoder, 5denotes a counter, 6 denotes a data extractor, 7 denotes a EOB (end ofblock) appending circuit, and 8 denotes an output terminal.

The video area in each track is divided into a main area for recordingthe bit stream of the ATV signal,and copy area for recording importantpart (HP data) of the bit stream which are used for reconstruction ofthe image in fast replay. Only the intra-encoded blocks are effectiveduring fast replay, so that they are recorded in the copy area. Toreduce the data further, the only the low-frequency components areextracted from all the intra-encoded blocks, and recorded as HP data.

The bit stream of MPEG2 is input via the input terminal 2, and led tothe recording format circuit 3. The bit stream from the input terminal 1is also input to the variable-length decoder 4, and the syntax of thebit stream of the MPEG2 is analyzed, and the intra-picture data isdetected, and timing signals are generated by the counter 5, and thelow-frequency components of all the blocks in the intra-picture data areextracted. Furthermore, EOBs are appended at the EOB appending circuit7, and HP data is constructed at the HP data format circuit 2. At therecording data format circuit 3, the HP data and the bit stream to berecorded in the main area are combined into a format suitable forrecording in one track, and output via the output terminal 8, andrespectively recorded in the main area and the copy area.

FIG. 44 shows a recording format on the tape. The combination of analphabetic character A, B, C, and succeeding numerals 0, 1, 2 indicatethe areas where HP data are recorded. Different data Ai, Bi, Ci (i=0, 1,2, . . . ) are recorded in each track. An identical set of data Ai, Biand Ci are repeatedly recorded over 17 tracks within a range indicatedby RP.

FIG. 45A and FIG. 45B show an example of replay system in a conventionaldigital VTR. FIG. 45A schematically shows normal replay. FIG. 45Bschematically shows fast replay.

Separation of data from the magnetic tape during normal replay and fastreplay are performed respectively in the following ways. During normalreplay, the bit stream recorded in the main areas 270 is all replayed,and the bit stream from the data separation circuit 272 are sent as thenormal replay data, to an MPEG2 decoder, provided outside the replaysystem. The HP data from the copy area 271 are discarded. During fastreplay, only the HP data from the copy area 271 are collected, and sent,as fast replay data, to the decoder. At the data separation circuit 272,the bit stream from the main areas 270 is abandoned.

A method of fast replay from a track in which a main area 270 and copyareas 271 is next described. FIG. 46A shows a scanning trace of a head.FIG. 46B shows a track regions from which the replay is possible. Whenthe tape speed is an integer multiple of the normal replay speed, ifphase-locking control is conducted by an ATF (automatic track following)method or the like for tracking by moving the head itself, the headscanning is in a predetermined phase relationship with tracks having anidentical azimuth. As a result, the data replayed by the head A from thetracks recorded alternately by the heads A and B, are fixed to thosefrom the meshed regions.

In FIG. 46B, if the signal having an output level larger than −6 dB isreplayed by the heads, the data is replayed by one head from the meshedtape regions. The drawing show an example of nine-time speed replay. Ifreplay of the signals from the meshed regions is ensured at thenine-time replay, the regions are used as copy areas, and the HP dataare recorded in the copy areas, so that the reading of the HP data fromthese regions at this speed is possible. However, reading of thesesignals at different speeds is not ensured. Accordingly, a plurality ofareas need to be selected for the copy areas, so that the replay signalscan be read at different tape speeds.

FIG. 47 shows regions where the copy areas overlap for a plurality ofdifferent replay speeds. It shows examples of scan regions for threedifferent tape speeds, for cases where the head is in synchronism with atrack of an identical azimuth. The scan regions where the reading by thehead is possible at different tape speeds overlap, at some of theregions. By selecting the regions at which the overlapping occurs as thecopy areas, reading of the HP data at different tape speeds can beensured. The drawings show the regions at which overlapping occurs atthe feed-forward at four-time, nine-time, 17-time speed. Theses scanregions are identical to those of feed-forward at −2 time, −7 time and−15 time high speeds (i.e., rewind at 2 time, 7 time and 15 timespeeds).

Even though there are overlapping regions for different tape speeds, itis not possible to determine a recording pattern so that identicalregions are always traced at different speeds. This is because thenumber of tracks crossed by the head differ depending on the tape speed.Moreover, it is necessary for the head to be capable of starting tracingat whichever identical azimuth track. For this reason, identical HP datais repeatedly recorded over a plurality of tracks, to solve the aboveproblem.

FIG. 48 shows examples of scanning traces of the rotary head atdifferent tape speeds. Regions 1, 2 and 3 are selected from among theoverlapping regions for five-time and nine-time speeds. If identical HPdata are repeatedly recorded over 9 tracks (over 9 tracks within therange indicated by RP in FIG. 48), the HP data can be read at five-timeand nine-time speeds.

FIG. 49A and FIG. 49B show scanning traces at five-time speed replay. Inthe illustrated example, identical HP data is repeatedly recorded overfive consecutive tracks (within the region indicated by RP). As will beseen from the drawings, identical HP data is recorded over the number oftracks identical to the number of times of the tape speed (i.e., 5). Ineither of case 1 and case 2, either the head A or B can read HP datafrom corresponding azimuth track. Accordingly, providing the copy areasin each track, in a number identical to the number of times of the tapespeed at the fast replay, and repeatedly recording the HP data there,the copied HP data can be read at various speeds, and in either theforward or reverse direction.

In the manner described, the special replay data is recorded in the copyareas, repeatedly, to improve the picture quality during the specialreplay in the transparent recording system.

FIG. 50 shows a recording format on a track in a conventional digitalVTR. Main areas 270 and copy areas 271 are provided in one track. In aconsumer digital VTR, a video area in each track has 135 sync blocks(SB), and 97 sync blocks are assigned to main areas and 32 sync blocksare assigned to copy areas. The sync blocks at the regions correspondingto the 4-, 9- and 17-time speed shown in FIG. 47 are selected for thecopy areas. The data rate of the main areas is about 17.46 Mbps(97×75×8×10×30), and the data rate of the copy areas where identicaldata is repeated 17 times is about 338.8 kbps (32×75×8×10×30/17).

The convention VTR described above has the following problems.

In the conventional VTR, in any of the cases of the low-speed replay of2- to 4 time speed, and the case of a fast replay of more than 9-timespeed, the data of the copy areas consisting of the predetermined numberof sync blocks contained in a common overlapping areas is read and usedfor replay. As a result, the deterioration in the picture quality whichis not conspicuous in a high-speed fast replay, in which the change ofthe scene is quick, shows up in a lower-speed replay, in which thechange is of the scene is slow.

In the convention device, the areas where the copy areas overlap aredetermined without taking account of the regions where the reading ispossible in slow replay or still replay. As a result, when slow or stillreplay is conducted in the conventional device, the reading from thecopy areas is not necessary ensure. Moreover, the picture is notreconstructed from only the HP data in the copy areas, so that thepictures of slow or still replay are not obtained.

When a bit stream from the main areas is used during slow or stillreplay, some regions may not be scanned, or the replay output may beinsufficient, so that replay data is not obtained from some regions.Thus, replay of data from all the areas is not ensured, and slow orstill replay pictures of good quality cannot be obtained.

In the conventional device, where each transport packet is divided andrecorded in a plurality of sync blocks on the tape, the positions atwhich the packet is divided and the number of sync blocks into which thepacket is divided are not constant because of the image compression.That is, depending on the characteristics of the picture, the amount ofdata contained may vary and the length of each packet may vary. For thisreason, when the transport packet is divided and recorded in many syncblocks, it is affected easily by data errors for each sync blockassociated with the magnetic recording and replay.

More specifically, assume that a packet of a length of 188 bytes isdivided and recorded in consecutive sync blocks of a length of 77 bytes.Generally, the ratio between the length of the packets and the length ofthe sync block is not an integer. The number of sync blocks for eachpacket differs. The position at which the packet is divided also varies,and accordingly, the number of sync blocks into which the packet isdivided varies between 3 and 4.

When digital data is magnetically recorded or replayed, data errors foreach sync block occurs. If the data in the replayed packet contains anerror, it cannot be used. A packet which is divided into four syncblocks has a higher probability of being erroneous than a packet whichis divided into three sync blocks.

When data used for fast replay is used, by reducing the amount of datafrom ordinary encoded data, no control is made to maintain that the dataof the image blocks is recorded at a predetermined number of syncblocks. Accordingly, when data of frame picture for high-speed replay isrecorded in a plurality of sync blocks on a magnetic tape, the encodeddata of the image blocks is divided at the boundaries between the syncblocks. As a result, the blocks recorded being divided is easilyaffected by the data errors for each sync block, associated with themagnetic recording and replay.

When image block data of a 50 byte length is recorded, it may berecorded within a single sync block, or it may be divided into two syncblocks. In comparison with the case where recording is in one sync blockonly, if the recording is into two sync blocks, the effect of errors foreach sync block associated with recording and replay is twice.

Moreover, the positions at which the fast replay data is recorded aredetermined on the basis of the head scanning traces at a specific fastreplay speed. As a result, fast replay is not possible at speeds otherthan the specific fast replay speed.

Furthermore, the copy areas where the fast replay data is recorded aredisposed on the tracks such that reading from them can be madecorrectly. However, slow replay is not taken account of, so that it isnot sure whether data is read correctly. Thus, the conventional devicedoes not have any assurance with regard to the picture quality of slowreplay.

Moreover, when still replay is selected, the replay data is not read,and no still picture is correctly displayed.

Furthermore, with regard to the speed of the fast replay in theconventional device, even where identical copy data is recorded over 17tracks, odd-number multiple-speeds which can be selected are limited to+17-time speed, +13-time speed, +9-time speed, +5-time speed, −15-timespeed, −11-time speed, −7-time speed, and −3-time speed.

In order to check all the intra-picture data, the headers of the ATV bitsteams must be analyzed for each macro block.

SUMMARY OF THE INVENTION

The invention has been achieved to solve the problems described above,and its object is to provide a digital VTR with which the picturequality is higher in low-speed fast reply, than in middle- or high-speedfast replay.

Another object of the invention is to provide a digital VTR whichrecords a bit stream transmitted digitally, and with which slow or stillreplay picture of a good quality can be obtained even when slow or stillreplay is conducted.

Another object of the invention is to provide a digital VTR which isless affected by data errors associated with recording and replay.

A further object of the invention is to provide a digital VTR with whicha fast replay is possible at an arbitrary speed.

A further object of the invention is to provide a digital VTR whichrecords a bit stream transmitted digitally, and with which slow or stillreplay pictures of a good quality are obtained even if slow or stillreplay is conducted.

A further object of the invention is to provide a digital VTR with whichthe number of multiple-speeds which can be selected for fast replay canbe increased, and intra-picture data can be detected for each frame oreach field.

According to a first aspect of the invention, there is provided adigital VTR magnetically recording and replaying video and audio signalsat a recording data rate higher than a data rate of a bit stream whichis digitally transmitted, recording the bit stream on a magneticrecording medium, by dividing the data for one screen as a basebandvideo signal, into a plurality of tracks, comprising:

-   -   data extracting means for dividing a first low-frequency        component data from intra-encoded blocks of the bit stream, into        a predetermined number L (L being a positive integer not smaller        than 2) and extracting the divided low-frequency component, and        extracting a second low-frequency component data having        frequencies higher than the first low-frequency component data;        and    -   recording means for recording the first low-frequency component        data, being divided, in said predetermined number L of first        specific regions respectively disposed in a plurality of tracks        into which data for said one screen is divided, and recording        said second low-frequency component data in second specific        regions disposed in specific tracks of said plurality of tracks,        and recording all the bit stream in the remaining regions in        each track, other than said first and second specific regions.

With the above arrangement,

-   -   during normal replay, all the bit stream digitally transmitted        during recording can be replayed and used,    -   during middle-speed and high-speed fast replay, the first        low-frequency component recorded in the first specific regions        is replayed, and    -   during low-speed fast replay, the second low-frequency component        recorded in the second specific regions on the specific tracks        and the first low-frequency component recorded in the first        specific regions are replayed and used.

Accordingly, the first HP data D1 is recorded in the first specificregions and the second HP data D2 is recorded in the second specificregions in the specific tracks, within the range of data rate not largerthan the remaining data rate after subtracting the date rate forrecording the bit stream, so that it is possible to cope not only withthe normal replay, but also with low-speed fast replay, and middle-speedand high-speed fast replay, in which the pictures are formed only ofintra-encoded blocks, and the pictures of a better quality is obtainedin the low-speed fast replay than in the middle-speed and high-speedfast replay.

The digital VTR of the first aspect of the invention may furthercomprise:

-   -   selecting means for selecting one of a normal replay and fast        replays of a plurality of speeds, by varying the transport speed        of the magnetic recording medium;    -   control means for causing, when the fast replay at a low-speed        is selected by said selecting means, the transport speed of the        magnetic recording medium to be periodically alternated between        a speed near the standard speed for the normal replay and a        speed near the speed for the low-speed fast replay; and    -   replay means for replaying, at the speed near the standard        speed, at least the second low-frequency component data recorded        in said specific regions from said specific tracks, and the        first low-frequency component data recorded in said first        specific regions in said specific tracks.

With the above arrangement,

-   -   in the middle-speed or high-speed fast replay, the magnetic        recording medium is made to run continuously at a middle-speed        or high-speed fast replay speed, so that the first low-frequency        component data is collected and replayed from a plurality of        tracks, and    -   in the low-speed fast replay, at least the second low-frequency        component recorded in the second specific regions in the        specific tracks which can be obtained during transport at a        speed near the normal replay speed, and the first low-frequency        component recorded in the first specific regions in the specific        tracks are replayed as fast replay data.

Accordingly, the bit stream digitally transmitted for recording can allbe replayed during normal replay, so that there is no degradation in thepicture quality. In the middle-speed and high-speed fast replay,although the picture quality is lower than in the normal replay, it ispossible to cope with search of the recorded contents, and the like.

Moreover, in a replay of a low speed, of about twice the normal speed,the magnetic tape is alternately transported at a speed near thestandard speed for normal replay, and a speed near the low-speed fastreplay speed, and at the speed near the standard speed, at least thesecond low-frequency component data recorded in the second specificregions in the specific tracks, and the first low-frequency componentdata recorded in the first specific regions are all replayed, so thatalthough the resolution of the high-frequency region is lost, comparedwith the normal replay, the pictures with a better quality than in themiddle-speed and high-speed fast replay can be obtained.

According to a second aspect of the invention, there is provided adigital VTR for magnetically recording and replaying a bit streamdigitally transmitted, comprising:

-   -   detecting means for detecting intra-picture data in the bit        stream that are replayed;    -   extracting means for extracting the intra-picture data from the        replayed bit stream, according to the result of the detection at        the detecting means;    -   replay mode designating means for selecting and designating one        of the normal replay, slow replay and still replay, as a replay        mode; and    -   replay data outputting means for storing the extracted        intra-picture data, and outputting the intra-picture data as the        replay picture data, according to the mode signal output by said        replay mode designating signal.

With the above arrangement

-   -   during replay with a digital VTR for recording and replaying a        bit stream digitally transmitted, the intra-picture data in the        bit stream that is replayed is detected, and intra-picture data        is extracted from the replayed bit stream on the basis of the        result of the detection, and the intra-picture data is stored,        and output as the replay picture data according to the replay        mode signal,    -   so that even when the replay mode is slow replay, or still        replay, the stored intra-picture data can be output as the        replay data, and slow or still replay pictures with a good        quality can be obtained.

In the digital VTR of the second aspect of the invention, it may be soarranged that said replay data output means comprises:

-   -   address detecting means for detecting an address of the track at        which the intra picture data is recorded;    -   control means for causing normal speed replay and rewinding, for        reverse control, on the basis of the result of the detection of        the address of the track.

With the above arrangement,

-   -   when the replay mode signal designates slow replay or still        replay, and the normal speed replay and rewinding are conducted        alternately for slow replay,    -   the intra-picture data in the bit stream during normal speed        replay is detected, and the intra-picture data is extracted from        the replayed bit stream on the basis of the result of the        detection, and the intra-picture data is stored, and the address        of the recording track where the intra picture data is recorded        is detected, and the reverse control is conducted on the basis        of the result of the detection, and the stored intra-picture        data is output as the replay picture data,    -   so that when the designated replay mode is slow replay or still        replay, the stored intra-picture data is output as the replay        data, and slow or still replay pictures of a good quality are        obtained.

Accordingly, the stored intra-picture data can be output as the replaydata, during slow or still replay, so that slow or still replay picturesof a good quality can be obtained.

In the digital VTR of the second aspect of the invention, said replaydata output means may comprise:

-   -   control means for stopping the tape for a predetermined period        after all the intra-picture data is extracted from the bit        stream by normal speed replay.

With the above arrangement,

-   -   when normal speed replay and halting are conducted        intermittently, as replay mode signal indicates slow replay,    -   the intra-picture data in the bit stream during normal speed        replay is detected, and the intra-picture data is extracted from        the replayed bit stream, and stored, and after all the        intra-picture data is extracted, the tape is halted for a        predetermined period, and the stored intra-picture data is        output as the replay picture data,    -   so that when the designated replay mode is slow replay, the        intra-picture data is output as the replay data, whereby slow        replay pictures with a good quality are obtained.

According to a third aspect of the invention, there is provided adigital VTR for magnetically recording and replaying digitallytransmitted bit stream in a predetermined recording format, a magneticrecording and replaying device comprising:

-   -   division number setting means responsive to a bit stream input,        a predetermined number M (M being a positive integer) of        transport packets as a unit, for setting the division number N        (N being a positive integer, N≠M) into sync blocks which are to        form the recording format;    -   header appending means for appending, to data of the bit stream        before the division, a header indicating the transport packet;        and    -   format forming means for forming N consecutive sync blocks from        the data after the division of the bit stream.

With the above arrangement,

-   -   the predetermined number M of packet data are divided into and        recorded in the predetermined number N of the sync blocks. For        instance, when the size of the packet is 188 bytes, and the data        capacity of the sync block is 77 bytes, 376 bytes, which is        twice 188 bytes, is smaller than 376 bytes, which is five times        77 bytes, so that M is set to 2 and N is set to 5, and two        packets are recorded in five sync blocks. There are four        boundaries between five consecutive sync blocks, and each of the        packet data extends across the boundaries at two locations, and        not at three or more locations.

Accordingly, when transparent recording is effected, the the number ofunits into which the packets of the bit stream is divided can be madesmall on average, and the probability of the entire packet beingrendered erroneous because of the data error due to recording and replaycan be minimized.

According to fourth aspect of the invention, there is provided a digitalVTR for magnetically recording and replaying a digitally transmitted bitstream in a predetermined recording format, comprising:

-   -   decoding means for decoding the content of data of an input bit        stream;    -   data extracting means for extracting a series of encoded data        used for fast replay, on the basis of the decoded data; and    -   data reducing means for reducing the data amount of the        extracted encoded data to a data amount which can be recorded in        K sync blocks (K being a positive integer) in said predetermined        format.

With the above arrangement,

-   -   when encoded data used for fast replay is formed from original        data, by reducing the data amount,    -   the data amount after the reduction is of such a size which can        be recorded in a predetermined number of sync blocks, and the        data is recorded in the predetermined number of sync blocks.

Accordingly, the number of units into which block data is divided whenthe fast replay data is recorded on the tape can be minimized onaverage, so that the probability of the entire block data beingerroneous because of data error due to recording and replay can beminimized.

In the digital VTR of the fourth aspect of the invention, it may be soarranged that said encoded data is recorded repeatedly for a number oftimes about twice the multiplier of the maximum fast replay speed(maximum speed at which the fast replay is possible).

With the above arrangement,

-   -   the encoded data for fast replay is recorded repeatedly on        consecutive tracks a number of times which is about twice the        multiplier of the fast replay speed,    -   so that either of the heads of the different azimuths scans the        recording regions of the encoded data for fast replay at least        once, even when the replay is made with the maximum speed at        which replay is possible.

If the heads on the drum are disposed in opposition, 180° apart, thetape is wrapped around the drum over about 180°, and the speed of themaximum fast replay is an even multiple speed, the first and secondazimuth heads supplement, each other, the data that cannot be replayedby each of the heads, alone.

All the replay encoded data can be reproduced, and the fast replay canbe conducted at any arbitrary even multiple speed. The fast replay in areverse direction is also possible, at any arbitrary even multiplespeed.

According to a fifth aspect of the invention, there is provided adigital VTR for magnetically recording and replaying a digitallytransmitted bit stream, comprising:

-   -   detecting means for detecting intra-picture data in an input bit        stream;    -   forming means for forming fast replay data from the        intra-picture data;    -   header appending means for appending a first header for        discriminating the fast replay data from normal replay data, and        a second header for discriminating, within said normal replay        data, the intra-picture data and non-intra-picture data from        each other, and    -   recording means for recording the fast replay data together with        the normal replay data on a magnetic recording medium.

With the above arrangement,

-   -   in a device for recording and replaying a digitally transmitted        bit stream,    -   at the time of recording, intra-picture data is detected from        the input bit stream, and fast replay data is formed, and a        first header for discriminating the normal replay data and the        fast replay data from each other, a second header for        discriminating, within the normal replay data, the intra-picture        data and non-intra-picture data from each other, are appended        before recording. Accordingly, during normal replay, normal        replay data is selected from the data having been read,        according to the first header, and output.

The data output respectively for normal replay and fast replay, cantherefore be smoothly selected.

The digital VTR of the fifth aspect of the invention may furthercomprise:

-   -   replay means for replaying normal replay data, together with        fast replay data from the magnetic recording medium;    -   separating means for separating the normal replay data, by        checking the first header appended to the replay data from the        magnetic recording medium;    -   storage means for storing the intra-picture data, by checking        the second header appended to the normal replay data selected by        the separating means; and    -   switching means for selectively outputting the normal replay        data or the intra-picture data stored in the storage means,        depending on whether the replay mode is the normal replay or the        still replay.

With the above arrangement,

-   -   the normal replay data is selected and separated from the data        having been read during normal replay, according to the first        header,    -   only the intra-picture data is extracted from the normal replay        data according to the second header, and stored,    -   so that, during still replay, the normal replay data is selected        and output from the storage means. As a result, satisfactory        still replay can be achieved.

The second headers for discriminating between the intra-picture data andnon-intra-picture data are appended to the transport packets which arenormal replay data before recording, so that the detection of theintra-picture data during still replay is facilitated.

Moreover, the intra-picture data detected according to the second headerduring normal replay is stored, and output when still replay isselected, so that switching to the still replay mode is achieved withease.

The digital VTR of the fifth aspect of the invention may furthercomprise:

-   -   replay means for replaying normal replay data together with the        fast replay data from the magnetic recording medium;    -   separating means for separating the normal replay data, by        checking the first header appended to the replay data from the        magnetic recording medium;    -   storage means for storing the intra-picture data, by checking        the second header appended to the normal replay data selected by        said separating means; and    -   switching means for selectively outputting the normal replay        data or the intra-picture data stored in the storage means,        depending on whether the replay mode is the normal replay or the        slow replay.

With the above arrangement,

-   -   during slow replay, the normal replay data is selected and        separated according to the first header, and    -   only the intra-picture data is extracted from the normal replay        data according to the second header,    -   so that, by selectively outputting the normal replay data from        the storage means, satisfactory low-speed replay can be        achieved.

The intra-picture data detected according to the second header isrecorded during slow replay, and intra-picture data is selected andoutput, so that slow replay can be achieved with ease.

Moreover, the transport packets which are the normal replay data arerecorded, after having appended second headers for discriminating theintra-picture data and non-intra-picture data from each other, so that,during slow replay, detection of the intra-picture data is achieved withease.

The digital VTR of the fifth aspect of the invention may furthercomprise:

-   -   replay means for replaying normal replay data together with the        fast replay data from the magnetic recording medium;    -   separating means for separating the fast replay data from the        normal replay data, by checking the first header appended to the        replay data from the magnetic recording medium; and    -   switching means for selectively outputting the normal replay        data or the high-speed data, depending on whether the replay        mode is the normal replay or the fast replay.

With the above arrangement,

-   -   during fast replay, the fast replay data can be selected and        output with ease, from the data having been read, according to        the second header.

Because the first header for discriminating the transport packets withwhich normal replay is possible, and fast replay data from each other,selection of the data output respectively during normal replay and fastreplay can be made smoothly.

According to a sixth aspect of the invention, there is provided adigital VTR for magnetically recording and replaying a digitallytransmitted bit stream, comprising:

-   -   means for forming HP data for fast replay, by extracting        low-frequency component from intra-encoded data of an input bit        stream;    -   pattern generating means for forming a recording pattern for        recording the HP data, being divided, and a plurality of times,        in copy areas respectively set in J tracks (J=12×I+5, I being a        positive integer) forming one track group; and    -   recording means for recording in the formats according to the        recording patterns, partitioning one track into a main area in        which only said bit stream is recorded, and a plurality of copy        areas in which said HP data is recorded, being divided;    -   wherein the recording patterns of the HP data A, B and C        recorded, being divided into the N tracks include    -   a pattern TP1 in which HP data B is recorded in the copy area at        the center of the track, and HP data A is recorded in the copy        areas at both ends of the track,    -   a pattern TP2 in which HP data A is recorded in the copy area at        the center of the track, and HP data C is recorded in the copy        areas at both ends of the track,    -   a pattern TP3 in which HP data A is recorded in the copy areas        at the center and both ends of the track,    -   a pattern TP4 in which HP data C is recorded in the copy area at        the center of the track, and HP data A is recorded in the copy        areas at both ends of the track,    -   a pattern TP5 in which HP data B is recorded in the copy area at        the center of the track, and HP data C is recorded in the copy        areas at both ends of the track, and    -   a pattern TP6 in which HP data B is recorded in the copy areas        at the center and both ends of the track, and    -   in one track group,    -   a first track of pattern TP4 is disposed in the center of the        track group,    -   a second track of pattern TP1 is disposed at one end of the        track group,    -   a third track of pattern TP6 is disposed at the opposite end of        the track group,    -   tracks of patterns TP2 and TP3 are alternately and repeatedly        disposed between the first track and the second track,    -   tracks of patterns TP5 and TP6 are alternately and repeatedly        disposed between the first track and the third track.

With the above arrangement, when 1 track group is formed of 17 tracks,the recording format permits the multiplier of the fast replay speed tobe, in addition to +17, +13, +9, +5, −15, −11, −7, and −3, as in priorart, 3, 7, −5, and −1.

It is thus possible to form a recording format by which, by disposingthe HP data, the number of multiple-speeds which can be selected for thefast replay can be increased.

According to a seventh aspect of the invention, there is provided adigital VTR for magnetically recording and replaying a digitallytransmitted bit stream, comprising:

-   -   means for forming HP data for fast replay, by extracting        low-frequency component from intra-encoded data of an input bit        stream;    -   pattern generating means for forming a recording pattern for        recording the HP data, being divided, and a plurality of times,        in copy areas respectively set in J tracks (J=12×I+5, I being a        positive integer) forming one track group; and    -   recording means for recording in the formats according to the        recording patterns, partitioning one track into a main area in        which only said bit stream is recorded, and a plurality of copy        areas in which said HP data is recorded, being divided;    -   wherein the recording patterns of the HP data A, B and C        recorded, being divided into the N tracks include    -   a pattern TP1 in which HP data B is recorded in the copy area at        the center of the track, and HP data A is recorded in the copy        areas at both ends of the track,    -   a pattern TP2 in which HP data A is recorded in the copy area at        the center of the track, and HP data B is recorded in the copy        areas at both ends of the track,    -   a pattern TP3 in which HP data A is recorded in the copy areas        at the center and both ends of the track,    -   a pattern TP4 in which HP data A is recorded in the copy area at        the center of the track, and HP data C is recorded in the copy        areas at both ends of the track,    -   a pattern TP5 in which HP data C is recorded in the copy area at        the center of the track, and HP data A is recorded in the copy        areas at both ends of the track,    -   a pattern TP6 in which HP data C is recorded in the copy areas        at the center and both ends of the track,    -   a pattern TP7 in which HP data C is recorded in the copy area at        the center of the track, and HP data B is recorded in the copy        areas at both ends of the track,    -   a pattern TP8 in which HP data B is recorded in the copy area at        the center of the track, and HP data C is recorded in the copy        areas at both ends of the track, and    -   a pattern TP9 in which HP data B is recorded in the copy areas        at the center and both ends of the track, and    -   in one track group,    -   a first track of pattern TP5 is disposed in the center of the        track group,    -   second and third tracks of pattern TP6 are disposed on both        sides of and adjacent to the first track of pattern TP5,    -   a fourth track of pattern TP5 is disposed adjacent the second        track of pattern TP6,    -   a fifth track of pattern TP7 is disposed adjacent the third        track, and on the opposite side of the fourth track of pattern        TP5, with respect to the first track,    -   a sixth track of pattern TP1 is disposed at the head or tail of        the track group, and on the same side of the first track as the        fourth track,    -   a seventh track of pattern TP2 is disposed next to the track of        pattern TP1, and on the same side of the first track as the        fourth track,    -   an eighth track of pattern TP9 is disposed at the tail or head        of the track group, and on the same side of the first track as        the fifth track,    -   tracks of patterns TP3 and TP4 are alternately and repeatedly        disposed between the seventh track and the fourth track,    -   tracks of patterns TP8 and TP9 are alternately and repeatedly        disposed between the eighth track and the fifth track.

With the above arrangement,

-   -   when 1 track group is formed of 17 tracks, the recording format        permits the multiplier of the fast replay speed to be, in        addition to +17, +13, +9, +5, −15, −11, −7, and −3, as in prior        art, 3, 7, −5, and −1.

It is thus possible to form a recording format by which, by disposingthe HP data, the number of multiple-speeds which can be selected for thefast replay can be increased.

In either of the sixth and seventh aspects of the invention, it may beso arranged that, in normal replay, the bit stream recorded in the mainarea is transmitted to a decoder as a replay signal, and, in fastreplay, a replay bit stream is formed from the HP data, and transmittedto the decoder as replay HP data.

With the above arrangement, when 1 track group is formed of 17 tracks,it is possible to perform replay at the speeds of +17-time, +13-time,+9-time, +5-time, −15-time, −11-time, −7-time, and −3-time, as in priorart, and, in addition, 3-time, 7-time, −5-time, and −1-time.

It is thus possible to increase the number of multiple-speeds which canbe selected for fast replay from a format used for recording with thedigital VTR.

In either of the sixth or seventh aspects of the invention, it may be soarranged that, wherein the intra-encoded blocks forming the HP databelong to intra-encoded frame or intra-encoded field.

With the above arrangement, detection of the intra-picture data whichforms the basis for forming the HP data recorded in the copy areas issimplified.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram showing a recording system of a digital VTR ofEmbodiment 1 of the invention;

FIG. 2 is a diagram showing a sync block forming a recording block;

FIG. 3 is a diagram showing a track format of recording data accordingto Embodiment 1;

FIG. 4 is a block diagram showing a replay system of a digital VTR ofEmbodiment 1 of the invention;

FIG. 5 is a diagram showing the state of transport of a magnetic tape inlow-speed fast replay;

FIG. 6 is a diagram showing the scanning trace of a head against aspecific track in a low-speed fast replay;

FIG. 7A to FIG. 7D are diagrams for explaining the memory controloperation in the low-speed fast replay;

FIG. 8 is a diagram showing the scanning trace of a head against aspecific track in a middle-speed or high-speed replay;

FIG. 9 is a block diagram showing a replay system of a digital VTR ofEmbodiment 2 of the invention;

FIG. 10 is a diagram for explaining the control operation in slowreplay;

FIG. 11 is a schematic diagram showing a GOP forming an MPEG2 bitstream;

FIG. 12 is a diagram showing the relationship between the tape transportspeed and the period when the intra-picture data is picked up, inEmbodiment 2;

FIG. 13A and FIG. 13B are diagrams for explaining the control operationin reverse slow replay in Embodiment 3;

FIG. 14 is a block diagram showing a replay system of a digital VTR ofEmbodiment 4 of the invention;

FIG. 15 is a diagram for explaining the control operation in slowreplay;

FIG. 16 is a diagram showing the relationship between the tape transportspeed and the period when the intra-picture data is picked up, inEmbodiment 4;

FIG. 17 is a block diagram showing a recording system of a digital VTRof Embodiment 5 of the invention;

FIG. 18A shows the encoded data and decoded data of the image block, forexplaining the decoding of the image block in a recording system;

FIG. 18B shows the configuration of the HP data for high-speed replay,for explaining the decoding of the image block in the recording system;

FIG. 19 is a flow chart showing the procedure of the decoding of theimage block in the recording system;

FIG. 20 is a diagram showing a recording pattern of the high-speedreplay data;

FIG. 21 is a diagram showing a packet recording pattern;

FIG. 22 is a diagram showing a recording track on a magnetic tape;

FIG. 23 is a block diagram showing a replay system of a digital VTR ofEmbodiment 5;

FIG. 24 is a diagram showing a track format and a head scanning patternthat result when double speed replay is conducted from a recorded tape;

FIG. 25 is a diagram showing a track and a head scanning pattern thatresult when four-time speed replay is conducted from a recorded tape;

FIG. 26A and FIG. 26B are diagrams showing the signal level obtainedwhen replayed by two different heads of different widths, and the trackregions where data is reproduced, in the track pattern of FIG. 25;

FIG. 27 is block diagram showing a recording system of a digital VTR ofEmbodiment 6 of the invention;

FIG. 28 is a diagram showing the data track format in the video area ofa digital VTR;

FIG. 29 is a diagram showing the configuration of a transport packetcontained in the bit stream;

FIG. 30 is a diagram showing the configuration of data of the main areasrecorded on the magnetic tape;

FIG. 31 is a diagram showing the data configuration of the copy areas;

FIG. 32 is a block diagram showing a replay system of a digital VTR ofEmbodiment 6;

FIG. 33 is a block diagram showing a recording system of a digital VTRof Embodiment 7 of the invention;

FIG. 34 is a diagram showing the recording pattern of HP data recordedon the tracks;

FIG. 35 is a diagram showing the pattern signal generated by the patternsignal generator;

FIG. 36 is a diagram showing the data configuration of a sync block;

FIG. 37 is a diagram showing the data configuration of a sync block;

FIG. 38 is a diagram showing a recording pattern of HP data recorded onthe tracks in Embodiment 8;

FIG. 39A and FIG. 39B are diagrams showing an example of replay systemof a digital VTR in Embodiment 8;

FIG. 40 is a diagram showing scanning traces of a rotary head during theseven-time speed replay;

FIG. 41 is a diagram showing a track pattern of a conventional consumerdigital VTR;

FIG. 42A shows scanning traces against tracks formed on the magnetictape in normal replay in a conventional digital VTR;

FIG. 42B shows scanning traces against tracks in a fast replay in theconventional digital VTR;

FIG. 43 is a block diagram showing an example of recording system of aconventional digital VTR capable of fast replay;

FIG. 44 is a diagram showing an example of data format of data recordedon the tracks in the prior art;

FIG. 45A is a schematic diagram showing normal replay in an example of areplay system of a conventional digital VTR;

FIG. 45B is a schematic diagram showing fast replay in the example of areplay system of the conventional digital VTR;

FIG. 46A is a diagram showing a scanning trace in a fast replay;

FIG. 46B is a diagram showing track regions where fast replay ispossible;

FIG. 47 is a diagram showing regions of the copy areas between differentfast replay speeds;

FIG. 48 is a diagram showing examples of scanning traces of a rotaryhead of different tape speeds;

FIG. 49A and FIG. 49B are diagrams showing the scanning traces of arotary head in five-time speed replay; and

FIG. 50 is a diagram showing scanning traces showing recording format onthe tracks of a conventional digital VTR.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

Embodiment 1 is for obtaining a replay picture with a good picturequality, in particular at the time of low-speed fast replay.

FIG. 1 is a block diagram showing a recording system of a digital VTR ofand embodiment of the invention. In the drawing, reference numeral 1denotes a bit stream input terminal, 4 denotes a variable-lengthdecoder, 5 denotes a counter, 6 denotes a data extracting circuit, 7denotes an EOB (end of block) appending circuit, 10 denotes an errorcorrection encoder, 11 denotes a recording signal processing circuitcomprising a modulating circuit and a recording amplifier, and 15denotes a magnetic head.

An MPEG2 bit stream is input via the input terminal 1 to the errorcorrection encoder 10, where error correction codes used during normalreplay are appended, and sync signals and ID information are alsoappended. The error correction codes used during normal replay consistfor example of a product code configuration, consisting of inner errorcorrecting codes and outer error correcting codes.

The bit stream via the input terminal 1 is also input to thevariable-length decoder 4, where the syntax of the MPEG2 bit stream isanalyzed, and variable-length encoded intra-picture data is detected,and the number of the data units is counted at the counter 5. Thecounter 5 provides the data extracting circuit 6 with timing signals forcommencing and terminating extraction of intra-encoded blocks. The dataextracting circuit 6 extracts all the intra-encoded blocks forming theintra-picture data, and extracts the low-frequency components of theintra-encoded blocks, in order to reduce the data. That is, the dataextracting circuit 6 applies DCT processing to the blocks of 8×8 pixelconfiguration in the intra-picture data, and extracts the low-frequencycomponent data of the DCT coefficients, consisting DC components andlow-frequency AC components in the horizontal and vertical spatialfrequency regions of the DCT coefficients.

The low-frequency component data extracted from the intra-picture datais the important part (hereinafter referred to as HP data) of the bitstream used for the reconstruction of the picture at the time of fast ormultiple-speed replay. At the time of extraction, the HP data is dividedinto two units of two special replay data, i.e., first HP data D1 andsecond HP data D2, and output via the data extracting circuit 6. Thedivision is so made that the first and second HP data D1 and D2respectively contain first and second low-frequency components, and thesecond HP data D2 contains AC components having higher frequencies thanthe first HP data D1. The EOBs are appended at the EOB appending circuit7 to the first and second HP data D1 and D2, and the first and second HPdata D1 and D2 with the EOBs appended is input to the error correctionencoder 10, as data for recording in the copy areas, and errorcorrection codes, sync signals and ID information which are used in fastreplay are appended to form recording blocks. The error correction codesof the recording blocks used during fast replay are of inner codesconfiguration.

The recording signal processing circuit 11 modulates the recordingblocks for the main and copy areas output from the error correctionencoder 10, and records via the magnetic head 15 on a magnetic recordingmedium, such as a magnetic tape (not shown).

FIG. 2 shows sync blocks forming the recording blocks. In the drawing,reference numeral 20 denotes a region for recording a sync signal, 21denotes a region for recording ID information (identificationinformation), such as recorded track address information, 22 denotes aregion for recording the data regarding the bit stream for the mainareas, or the first and second HP data for the copy areas, and 23denotes a region for recording error correction codes which are innercodes appended to the sync blocks.

FIG. 3 shows a track format of the recording data of Embodiment 1. Inthe drawing, each of reference marks A and B denotes the type of thetrack corresponding to the respective azimuth, and the tracks arehelical. That is, each track is helical-recorded alternately on themagnetic tape using heads of different azimuths. The regions denoted bymarks 1D1, 2D1, 3D1 are first specific regions where sync blocks for thefirst HP data D1 for the copy areas are recorded.

The first HP data is divided into and recorded in the first specificregions 1D1 to 3D1, at three specific locations on one track. An exampleof the division is such that ten sync blocks (hereinafter referred to asSBs) are allotted to the region 1D1, eight SBs are allotted to theregion 2D1, and seven SBs are allotted to the region 3D1. The SBsallotted to the regions 1D1 to 3D1 correspond to the overlapping regionscommonly head-traced at various fast replays like in the prior artexample, and SBs of 1D1 to 3D1 of the same content are repeatedlyrecorded over the number of tracks identical to the speed multiplier ofthe highest-speed replay speed. The term “multiplier” is used to meanthe ratio of the fast replay speed to the normal replay speed. This hasalready been described in detail in connection with the prior artexample, so its further description is omitted here. In this embodiment,however, the first HP data contained in the SBs of the regions 1D1 to3D1 are used only at a middle-speed fast replay, around 9-time speed, orof a higher-speed fast replay.

In FIG. 3, SBs for the second HP data D2 for the copy areas are disposedin the second specific region 1D2 which is indicated by hatching. Thissecond specific region 1D2 is positioned on a specific track, e.g., thefirst track TA, within ten recording tracks for one frame (where thefield frequency is 60 Hz) as a baseband video signal which is a basicspecification for a consumer digital VTR. In the example underconsideration, 1D2 is formed of 50 SBs, and contains much moreintra-picture data than 1D1 to 3D1, which contain 25 SBs in total. Inthis embodiment, this region 1D2 is used for a low-speed fast-replay, offor example around double-speed. In this specific track TA, 50 SBs for1D2 and 25 SBs for 1D1 to 3D1 are disposed. In the tracks other than thespecific track TA, 25 SBs for 1D1 to 3D1 are disposed as copy areas.

In the remaining regions, other than the first specific regions in eachtrack in FIG. 3, and the remaining regions other than the first andsecond specific regions, are the main areas, where all the SBs regardingthe MPEG2 bit stream are recorded, and replayed during normal replay. Inconsumer digital VTRs, the video area on each track is formed of 135SBs, so that the number of SBs for the bit stream in the main areas inthe specific track TA is 60 (=135−75), and is 110 (=135−25) in thetracks other than the specific track TA.

As described above with reference to FIG. 41 in connection with theprior art example, in a consumer digital VTR, data areas such as audioareas, not shown, are provided on the extensions of the video areas ineach track, and the 135 SBs do not occupy all the area of in the tapewidth direction. But FIG. 3 shows only the video areas.

FIG. 4 is a block diagram showing the replay system of a digital VTRwhich is an example of the invention. In the drawing, reference numeral15 denotes a replay magnetic head, 12 denotes a replay signal processingcircuit comprising a head amplifier and having functions of detectionand demodulation of the replay signals, 13 denotes an error correctiondecoder correcting the errors in the replay signal on the basis of theerror correction inner codes appended for each SB at the time ofrecording, and 14 denotes a memory having a capacity of constructing apicture (whole frame) at the time of fast replay, by collecting only thefirst and second HP data, or the first HP data only, from the copyareas. Reference numeral 30 denotes an output terminal for low-speedfast data, 32 denotes an output terminal for normal replay data, 40denotes a capstan motor, 41 denotes a capstan control circuit, 42denotes a system control circuit for switching between modes such asnormal replay mode, low-speed fast replay mode, and high-speed fastreplay mode, and 43 denotes a memory control circuit.

Description is now made of the operation of the fast replay at alow-speed, around a double speed, for example. FIG. 5 shows the scanningof tape transport at the time of the low-speed fast replay. FIG. 6 showsthe scanning trace of the head against a magnetic tape during alow-speed fast replay. Responsive to a mode signal designating alow-speed fast replay from the system control circuit 42, the capstancontrol circuit 41 causes the capstan motor 40 to rotates in accordancewith the tape speed control curve shown in FIG. 5. That is, the tapetransport speed is switched periodically at a certain interval, betweena speed which is a little higher than and near the standard speed whichis the normal replay speed, and a high speed, e.g., about three-timespeed. In the period (t0 to t1) for the speed a little higher than thestandard speed, tracking is so made along the specific track TA as shownin FIG. 6, to replay all the SBs including the 50 SBs for 1D2, 10 SBsfor the 1D1, 8 SBs for 2D1 and 7 SBs for 3D1. In the fast replay ofaround the double speed, fast replay data LP(n) consisting of 75 SBs areoutput via the output terminal 30.

FIG. 7A to FIG. 7D are diagrams showing the memory control operationduring the low-speed fast replay. FIG. 7A and FIG. 7B show the contentsof the input data written in the memory 14, and the control signal WE.FIG. 7C shows the content of the output data read from the memory 14,and FIG. 7D shows the time axis.

The data of 75 SBs replayed during low-speed fast replay, areerror-correction processed at the error correction decoder 13 using theerror correction inner codes, and flag information FC indicating whetherthe error is correctable or uncorrectable is output to the memorycontrol circuit 43. Input to the memory control circuit 43 from thecapstan control circuit 41 is a speed control information SC indicatingthe period (t0 to t1) for the speed a little higher than the standardspeed, and during such period, the control signal WE is provided so thatonly the SBs error-corrected at the error correction decoder 13, and soindicated by the flag information FC are written in the memory 14. Thememory control circuit 43 supplies the memory 14 with a control signalSE for continuously reading the previous fast data LP(n), until the nextperiod (t2 to t3) of a speed of a little higher than the standard speed,shown in FIG. 5, when fast replay data LP (n+1) of 75 SBs in totalregarding 1D2, 1D1, 2D1 and 3D1 on the next specific track TA isreplayed.

By repeating the above operation, during the low-speed fast replay, thelow-frequency component data which are important part in the bit streamfor reconstructing the picture during low-speed replay is read from thememory 14 as the first and second HP data D1 and D2, and output via theoutput terminal 2, and supplied to the MPEG2 decoder, not shown, andexternal to the digital VTR.

Next, description is made of the operation of the middle-speed replay,of for example around 9 time-speed.

FIG. 8 shows the scanning traces of the head against the specific tracksin the middle-speed or higher-speed fast replay. Responsive to the modesignal for middle-speed fast replay from the system control circuit 42,the capstan control circuit 41 causes the magnetic tape to betransported at a speed around nine times the standard speed. As in thenine-time speed in FIG. 48 of the prior art example, the magnetic head14 picks up 1D1, 2D1, 3D1 for the first HP data, from the overlappingregions traced commonly at various fast replay speeds, over a pluralityof tracks, so that 25 SBs in total are reproduced.

The 25 SB data replayed during the middle-speed replay iserror-correction processed at the error correction decoder 13 using theerror correction inner codes, and flag information FC indicating whetherthe data is correctable or uncorrectable is output to the memory controlcircuit 43. During the middle-speed replay, the magnetic tape istransported continuously at a speed around nine times the normal speed,so that the speed control information SC input to the memory controlcircuit 43 is disregarded, and only the middle-speed fast replay dataLP(n) consisting of SBs having been error-corrected at the errorcorrection decoder 13 and so indicated by the flag information FC (i.e.,correctable SBs) is written in the memory 14. The data LP(n) iscontinuously read until the next middle-speed replay data LP(n+1) isreplayed and written in the memory 14. The first HP data D1 as thelow-frequency component data which is an important part of the bitstream for reconstructing a picture of a fast replay is output via theoutput terminal 31, and sent to an MPEG decoder not shown and externalto the digital VTR.

The operation during fast replay at a speed higher than nine-time speedis identical to that described above, so its description is omitted.

The operation during normal replay is next described briefly. In FIG. 3,during the normal relay, all the SBs for the MPEG2 bit stream in themain areas which are the remaining regions of the respective tracks arereplayed. The replay data is error-corrected at the error correctiondecoder 13 using the inner codes and the outer codes, or amended (forconcealment), and is output via the output terminal 32, and sent to theMPEG2 decoder not shown and external to the digital VTR.

In the above description, the first one of the ten tracks for one frameperiod (where the field frequency is 60 Hz) is assigned to the specifictrack TA, as shown in FIG. 3. However, any other one of the ten tracksmay be assigned to the specific track, or two or more of the ten tracksmay be assigned to specific tracks. In the latter case, the specifictracks may be adjacent to each other or separated from each other.

In the above description, 50 SBs forming the second HP data D2 aredisposed collectively in the second specific region on a specific track.The 50 SBs forming the second HP data may be divided into units ofsmaller numbers of SBs, and disposed at different positions on thespecific tracks.

In the low-speed fast replay, the entire specific track TA is generallyhead-traced as shown in FIG. 6, so that the intra-encoded sync blocks inthe MPEG2 bit stream recorded in the remaining regions on the specifictrack TA can also be used. In that case, more intra-encoded data can beused than in the case described above, so that the picture of thelower-speed fast replay is further improved.

Embodiment 2

Embodiments 2, 3 and 4 described next are for obtaining the slow- andstill-replay pictures of a good quality in a bit stream recording andreplay device, such as a digital VTR.

Embodiment 2 is for implementing slow replay by means of a pre-rollmethod in which the replay system alternately conducts normal speedreplay and rewinding.

FIG. 9 is a block diagram showing the replay system of a digital VTR inEmbodiment 2. In the figure, reference numeral 58 denotes an inputterminal for inputting replay signals read by the head from the mainareas and copy areas of the tape, 59 denotes a replay signal processingcircuit for performing processing such as waveform equalization, signaldetection and modulation, and outputting the bit stream of the ATVsignal, and the HP data, 60 denotes a data separation circuit forseparating the input data into the bit stream from the main areas andthe HP data from the copy areas, and 61 denotes a track addressidentifying circuit for identifying the track address track replayedfrom the replay signal from the replay signal processing circuit 59, andoutputting a signal indicative of the track number. Reference numeral 62denotes a replay mode signal generator for generating a signalindicative of the replay mode of the respective one of the normalreplay, fast replay, slow replay and still replay, 63 denotes a controlcircuit for generating control signals, such as the ones for controllingthe tape transport during slow replay and still replay, and 64 denotesan output terminal for outputting the control signals from the controlcircuit 63 to the servo circuit.

Reference numeral 65 denotes a syntax analyzer for analyzing the syntaxof the MPEG2 bit stream from the main areas and detecting intra-picturedata, 66 denotes a counter, 67 denotes a data extractor for extracting,storing and outputting intra-picture data from the bit stream, 68denotes a selector for selecting the data according to the replay modesignal from the replay mode signal generator 62, and 69 denotes anoutput terminal for outputting the selected data to the MPEG2 decoder,provided outside the digital VTR.

The replay operation of the digital VTR of Embodiment 2 will next bedescribed in detail. During normal replay and fast replay, the replaysignal read by the head from the tape is input via the input terminal58, and sent to the replay signal processing circuit 59, where waveformequalization, signal detection and demodulation are performed, andoutput as the original ATV signal in the form of a bit stream and the HPdata. The data separation circuit 60 separates the replay data from thereplay signal processing circuit 59 into the bit stream from the mainareas and the HP data from the copy areas. The bit stream from the mainareas is output as the normal replay data, and the HP data from the copyareas is collected and output as the fast replay data, and they aresupplied to the selector 68. The the selector 68 selects, on the basisof the replay mode signal from the replay mode signal generator 62, thenormal replay data in the form of the bit stream from the main areasduring normal replay, and the fast replay data in the form of the HPdata from the copy areas during fast replay. The selected data is outputvia the output terminal 69 to the decoder, not shown.

The operation during slow replay in Embodiment 2 will next be described.

FIG. 10 shows the control operation in the slow replay. It is assumedthat the slow replay is achieved by a pre-roll method in which normalspeed replay and rewinding are alternately conducted. In the normalspeed replay during slow replay, the replay signal read by the head fromthe tape is input via the input terminal 58, and sent to the replaysignal processing circuit 59, where replay signal processings, such aswaveform equalization, signal detection and demodulation, are applied,and output as the bit stream forming the original ATV signal and the HPdata. At the data separation circuit 60, the replay data is separatedinto the bit stream from the main areas and the HP data from the copyareas, and the bit stream from the main areas is output as the normalreplay data, and the HP data from the copy areas is collected and outputas fast replay data. The replay data from the replay signal processingcircuit 59 is sent to the track address identifying circuit 61, and thedata indicating the address of the track from which the replay data isreplayed, and the signal indicative of the track number is output andinput to the control circuit 63.

The bit stream from the main areas, forming the normal replay data,output from the data separation circuit 60 is input to the syntaxanalyzer 65, where the intra-picture data in the bit stream is detected,and timing signals are generated by the counter 66, and theintra-picture data is extracted by the data extractor 67. The counter 66generates a timing signal Sa indicating that an intra-picture data hasbeen extracted, and supplies the timing signal Sa to the control circuit63.

FIG. 11 is a schematic diagram showing a GOP forming the MPEG2 bitstream. In the MPEG2 bit stream, an intra-picture data, which can bedecoded independently, without referring to other pictures, is presentat the head of each GOP. The syntax analyzer 65 therefore detects a GOPheader indicating the head of each GOP, and the counter 66 generates atiming signal. In this way, the intra-picture data immediatelysucceeding the GOP header can be extracted by the data extractor 67.

When the rotary drum is stopped in normal speed replay, the drum rotatesfor several tracks after a stop control signal is generated and untilthe drum is actually brought to a standstill, and when the replay isresumed by starting rotation of the rotary drum a certain servo pull-intime is required. The length of the intra-picture data in the MPEG2 bitstream having been variable-length encoded is not constant, and theperiod from the detection of intra-picture data to detection of nextintra-picture data is not constant. Accordingly, in the pre-roll method,the tape is rewound for a certain period from the end of the detectedintra-picture data, to ensure the detection of the next intra-picturedata.

Referring to FIG. 10, it is assumed that intra-picture data #1 isdetected at the track Nos. 1 to 11, forming the addresses of the replaytracks. The data extractor 67 extracts the intra-picture data #1, andstores the data, and sends the intra-picture data #1, as the slow replaydata, to the selector 68, while the replay mode signal from the replaymode signal generator 62 indicates slow-replay. Since the replay modesignal indicates slow replay, the selector 68 outputs the intra-picturedata #1 from the data extractor 67, to the output terminal 69.

The track address of the replay track for which the intra-picture data#1 has been detected is identified by the track address identifyingcircuit 61, and at the control circuit 63, on the basis of the signal Safrom the counter 66, the address of the track in which the intra-picturedata #1 is recorded is detected. As a result, the control circuit 63generates a control signal for stopping the transport of the tape, atthe address No. 11 of the last track from which the intra-picture data#1 is read. When this control signal is sent via the output terminal 64to the servo circuit, the tape transport is stopped, and the tape isrewound from the last track No. 11 from which the intra-picture data #1has been read, to a track (track No. 0) one track before the track atthe head intra-picture data #1, and then normal speed replay is againconducted. During the period t2 to t3 when the stopping and rewindingare conducted, the data extractor 67 outputs, as the slow replay data,the intra-picture data #1 having been read immediately before.

The MPEG2 bit stream is variable-length encoded, so that the length ofthe intra-picture data varies. That is, more than ten tracks (ten tracksforming a standard length for one frame in a consumer digital VTR) maybe required for recording the intra-picture data. However, in theillustrated example, it is assumed that the intra-picture data isrecorded over ten or eleven tracks.

FIG. 12 is a diagram showing the relationship between the tape transportspeed and the interval for the reading or extraction of theintra-picture data. In the illustrated example, the speed “1” is thenormal replay speed, and speed “0” represents the state in which thetape is at standstill. The reading or extraction of the intra-picturedata is conducted in a period of from time t0 to time t1.

As shown in FIG. 10, when the normal speed replay state is resumed (t3),the replay signal read by the head from the tape-is input via the inputterminal 58, and is sent to the replay signal processing circuit 59,where replay signal processings are applied, and the data separationcircuit 60 separates the replay data into the bit stream from the mainareas and the HP data from the copy areas, and output them. The replaydata from the replay signal processing circuit 59 is sent to the trackaddress identifying circuit 61, and the data indicating the trackaddress replayed from the replay data is identified, and the signalindicative of the track number is supplied to the control circuit 63.The bit stream from the main areas, which is the normal replay data fromthe data separation circuit 60 is input to the syntax analyzer 65, wherethe intra-picture data in the bit stream is detected, and the counter 66generates start and termination timing signals for extracting theintra-picture data. The data extractor 67 extracts the intra-picturedata, and the counter 66 generates a timing signal Sa indicating thatthe intra-picture data has been extracted. The timing signal Sa is inputto the control circuit 63. The control circuit 63 receives the trackaddress number identified by the track address identifying circuit 61,and the signal Sa indicating that the intra-picture data has beenextracted, and when the intra-picture data #2 next to the intra-picturedata #1 which was extracted previously is extracted, the control circuit63 detects the address of the track in which the intra-picture data #2is recorded, and at the last track where the intra-picture data isextracted, the control signal for stopping the tape transport isgenerated. When this control signal is supplied via the output terminal64 to the servo circuit, the tape transported is stopped.

Referring to FIG. 10, let us assume that the intra-picture data #2 ofthe tracks Nos. 51 to 62 is detected, next the intra-picture data #1.When the intra-picture data #2 is extracted, the data extractor 67stores the intra-picture data #2 in substitution for the intra-picturedata #1, and outputs the intra-picture data #2 as the slow replay data,to the selector 68. Since the replay mode signal indicates slow replay,the selector 68 outputs the data from the data extractor 67 to theoutput terminal 69. Responsive to the track address number from thetrack address identifying circuit 61 and the timing signal Sa indicatingthat the intra-picture data #2 has been detected, the control circuit 63generates a control signal for stopping the tape transport at the lasttrack of the address No. 62 where the intra-picture data #2 is read. Thetape is rewound from the last track with the address No. 62 where theintra-picture data #2 is read, to the track (track No. 50) one beforethe first track where the intra-picture data #2 starts, and normal speedreplay is again conducted. For the period (t6 to t7) when the stoppingand rewinding are conducted, the data extractor 67 outputs theintra-picture data #2 having extracted immediately before the stoppingas the slow replay data.

Next, the normal speed replay is again conducted, and the operationsimilar to that described above is repeated, and the slow replay is thuscontinued.

For still replay, like the slow replay, during the normal speed replay,intra-picture data in the bit stream from the main areas separated fromthe replay data, at the data separation circuit 60 is detected at thesyntax analyzer 65, and a timing signal is generated at the center 66,and the intra-picture data is extracted and stored at the data extractor67. When the tape is at a standstill, the intra-picture data extractedby the data extractor 67 immediately before is kept output as the stillreplay data.

As has been described, the normal speed replay and rewinding arealternately conducted, and the intra-picture data in the bit stream fromthe main areas, extracted during normal speed replay, is stored, andoutput as slow or still replay data. Reproduction of data for slow orstill replay is ensured, and slow or still replay pictures of a goodquality can be obtained.

Embodiment 3

In Embodiment 2, the pre-roll method was used, in which when forwardslow replay is performed, intra-picture data in the bit stream from themain areas is extracted during normal speed replay, and is stored, andused as image data during slow replay. The pre-roll method can besimilarly used in reverse slow replay. The intra-picture data in the bitstream from the main areas is extracted, and stored, and rearranged andoutput, and used as the image data for the slow replay.

FIG. 13A and FIG. 13B are explanatory diagrams for showing the controloperation in the reverse slow replay in Embodiment 3. FIG. 13A shows anexample of tracks in which track address and intra-picture data arerecorded on the tracks. It is assumed that the value of the trackaddress (track number) increases rightward, starting from the trackaddress No. 0. As in Embodiment 2, the reverse slow replay is performedby the pre-roll method, in which normal speed replay and rewinding areconducted alternately. It is assumed that the reverse slow replay isstarted from the track No. 290 in FIG. 13A.

First, normal speed replay is conducted starting at the track No. 290,and intra-picture data #4 recorded in the track Nos. 291 to 300 in thebit stream from the main areas is detected, and separated at the dataseparation circuit 60 in FIG. 9, and a timing signal is generated by thecounter 66, and the intra-picture data #4 is extracted and stored at thedata extractor 67 (t0 to t1). The data extractor 67 outputs theintra-picture data #4 as the reverse slow replay data, to the selector68. Because the replay mode signal indicates reverse slow replay, theselector 68 outputs the data from the data extractor 67 to the outputterminal 69. The counter 66 generates a timing signal Sa indicating thatthe intra-picture data #4 has been extracted, and supplies it to thecontrol circuit 63. The addresses of the tracks from which theintra-picture data #4 has been detected are identified by the trackaddress identifying circuit 61, and the addresses of the tracks wherethe intra-picture data #4 is recorded are detected at the controlcircuit 63, in accordance with the signal Sa from the counter 66. As aresult, the control circuit 63 rewinds the tape from the last track ofaddress No. 300 from which the intra-picture data has been detected, toa track No. 140 preceding by the number of tracks (160 tracks in thisexample) within which at least one other intra-picture data is recorded,and stops the tape (t1 to t2), and again conducts the normal speedreplay.

When the state of normal speed replay is resumed, as in the abovedescription, the bit stream from the main areas, forming the normalreplay data, output from the data separation circuit 60 is input to thesyntax analyzer 65. The syntax analyzer 65 detects the intra-picturedata #3 recorded in the track Nos. 151 to 160, from the bit stream, andthe counter 66 generates starting and terminating timing signals forextracting the intra-picture data. The data extractor 67 extracts theintra-picture data #3, and the counter 66 generates a timing signal Saindicating that the intra-picture data has been extracted, and suppliesit to the control circuit 63. The control circuit 63 receives the trackaddress number identified by the track address identifying circuit 61,and the signal Sa from the counter 66 indicating that the intra-picturedata has been extracted, and when the intra-picture data #3 isextracted, the control circuit 63 detects the address of the track wherethe intra-picture data #3 is recorded, and stores the number of the lasttrack from which the intra-picture data #3 is extracted, and generates acontrol signal to stop the tape at the last track No. 300 from which theprevious intra-picture data #4 was extracted (t2 to t3). This controlsignal is supplied via the output terminal 64 to the servo circuit, sothat the tape is stopped.

When the intra-picture data #3 is extracted, the data extractor 67substitutes the intra-picture data #3 for the intra-picture data #4,andoutputs the intra-picture data #3 as the reverse replay data, to theselector 68. Since the replay mode signal indicates the reverse slowreplay, the selector 68 outputs the data from the data extractor 67 tothe output terminal 69. Then, the tape is rewound to a track No. 0,which is 160 tracks preceding, by 160 tracks within which at least oneother intra-picture data is recorded, the last track No. 160 from whichthe intra-picture data #3 was extracted, and is stopped (t3 to t4), andthen normal speed replay is again conducted.

When the state of normal speed replay is resumed, as in the abovedescription, the bit stream from the main areas output from the dataseparation circuit 60 is input to the syntax analyzer 65. The syntaxanalyzer 65 detects the intra-picture data #1 recorded in the track Nos.1 to 11, from the bit stream, and the counter 66 generates starting andterminating timing signals for extracting the intra-picture data. Thedata extractor 67 extracts the intra-picture data #1, and the counter 66generates a timing signal Sa indicating that the intra-picture data hasbeen extracted, and supplies it to the control circuit 63. The controlcircuit 63 receives the track address number identified by the trackaddress identifying circuit 61, and the signal Sa from the counter 66indicating that the intra-picture data #1 has been extracted, and whenthe intra-picture data #1 is extracted, the control circuit 63 detectsthe address of the track where the intra-picture data #1 is recorded,and stores the number of the last track from which the intra-picturedata #1 is extracted.

The normal speed replay is continued, and the intra-picture data #2 inthe bit stream recorded in the track Nos. 51 to 62 is detected, and thecounter 66 generates a timing signal, and the data extractor 67 extractsand stores the intra-picture data #2, and a control signal for stoppingthe tape transport is generated at the last track No. 160 of theintra-picture data #3 of the previous normal speed replay (t4 to t5).This control signal is sent via the output terminal 64 to the servocircuit, so that the tape transport is stopped.

When the intra-picture data #1 and #2 is extracted, the data extractor67 rearranges the data by reversing the order, and substitutes, for theintra-picture data #3, the intra-picture data #2 and then theintra-picture data #1, and successively outputs them as the slow reversedata, to the selector 68. Since the replay mode signal indicates thereverse slow replay, the selector 68 outputs the data from the dataextractor 67 to the output terminal 69.

Then, the normal speed replay is conducted, and the operation similar tothat described above is repeated. The reverse slow replay is continuedin this way.

In this way, normal speed replay and rewinding are alternatelyconducted, and the intra-picture data in the bit stream from the mainareas extracted during normal speed replay is stored, and while tape isrewound to a track preceding the track from which the normal speedreplay was started, the intra-picture data is rearranged and output, andused as the image data for the reverse slow replay. Thus, the data forthe reverse slow replay is ensured, and a replay picture of a goodquality is obtained, and effects similar to those of Embodiment 2 areobtained.

Embodiment 4

FIG. 14 is a block diagram showing a replay system of a digital VTR ofEmbodiment 4 of the invention. In the drawing, reference numerals 58 to60, 62, and 64 to 69 are identical to those in the device of Embodiment2. Reference numeral 70 a control circuit for generating signals forcontrolling tape transport, and the like during slow and still replays,and the control signals are supplied to a servo circuit.

Intermittent drive for intermittently conducting normal speed replay andstopping to achieve slow replay will next be described. The operationsfor the normal replay and the fast replay are identical to those inEmbodiment 2, and their description is omitted.

FIG. 15 is an explanatory diagram showing the control operation duringslow replay. The replay signal read by the head from the tape at thenormal replay speed, during the slow replay, is input via the inputterminal 58, and sent to the replay signal processing circuit 59, wherereplay signal processings, such as waveform equalization, signaldetection and modulation, are applied, and output as the bit stream ofthe original ATV signal and the HP data. The data separation circuit 60separates the replay data into the bit stream from the main areas andthe HP data from the copy areas, and outputs the bit stream from themain areas as the normal replay data, and collects and outputs the HPdata from the copy areas as the fast replay data. The bit stream fromthe main areas forming the normal replay data, output from the dataseparation circuit 60 is input to the syntax analyzer 65, where theintra-picture data in the bit stream is detected, and the counter 66generates a timing signal, and the data extractor 67 extracts theintra-picture data #1 (t0 to t1). The counter 66 generates a timingsignal Sa indicating that the intra-picture data has been detected, andsupplies it to the control circuit 70.

As was described in connection with Embodiment 2, the MPEG2 bit streamis formed of a GOP (group of pictures) shown in FIG. 11, and theintra-picture data which can be decoded independently without referringto other pictures is present at the head of the GOP. Accordingly, thesyntax analyzer 65 detects the GOP header indicating the beginning ofthe GOP, and the counter 66 generates a timing signal, and theintra-picture data immediately after the GOP header is extracted at thedata extractor 67.

Referring to FIG. 15, let us assume that the intra-picture data #1 isextracted at the track Nos. 1 to 11. The data extractor 67 extracts andstores the intra-picture data #1, and sends the data as the slow replaydata to the selector 68 while the replay mode signal from the replaymode signal generator 62 indicates slow replay. Since the replay modesignal indicates slow replay, the selector 68 outputs the data from thedata extractor 67 to the output terminal 69.

When the extraction of the intra-picture data #1 is completed, thecounter 66 supplies the control signal 70 with a signal Sa indicatingthat the intra-picture data #1 has been extracted. The control signal 70then generates a signal for stopping the tape transport, so that thetape transport is stopped. The tape is halted for a period (t2 to t3)corresponding to the speed of the slow replay, and then normal speedreplay is conducted again. While the tape is halted, the data extractor67 outputs the intra-picture data #1 extracted immediately before, asthe slow replay data.

FIG. 16 shows the relationship between the tape transport speed and theperiod of extraction of the intra-picture data in Embodiment 4. Thetransport speed “1” represents the normal replay speed, and transportspeed “0” represents the state in which the speed “zero”, i.e., thestate in which the tape is halted. The extraction of the intra-picturedata is conducted for a period from time t4 to t5 in the drawing. Thatis, the extraction of the intra-picture data after time t2 when the tapetransport is stopped is conducted for a period of from time t4 to timet5. At time t3, when the normal speed replay state is resumed, thereplay signal read by the head from the tape is input via the inputterminal 58, and sent to the replay signal processing circuit 59, wherereplay signal processings are applied. The data separation circuit 60separates the replay data into the bit stream from the main areas andthe HP data from the copy areas, and outputs them. The bit stream fromthe main areas, forming the normal replay data, output from the dataseparation circuit 60, is input to the syntax analyzer 65, which detectsthe intra-picture data in the bit stream. The counter 66 generatestiming signals for extracting the intra-picture data. The data extractor67 extracts the intra-picture data, and the counter 66 generates atiming signal Sa indicating that the intra-picture data has beenextracted, and supplies it to the control circuit 70. On the basis ofthe signal Sa from the counter 66, indicating that the intra-picturedata has been detected, the control circuit 70 generates a controlsignal for stopping the tape transport when the intra-picture data #2next to the intra-picture data #1 that is extracted previously. Thiscontrol signal is sent via the output terminal 64 to the servo circuit,so that the tape transport is stopped.

Referring to FIG. 15, let us assume that the intra-picture data #2 isextracted at the track Nos. 51 to 62, after the intra-picture data #1.When the intra-picture data #2 is extracted, the data extractor 67replaces the intra-picture data #1 with intra-picture data #2, andoutputs the intra-picture data #2 as the slow replay data, and sends theintra-picture data #2 to the selector 68. Since the replay mode signalindicates slow replay, the selector 68 outputs data from the dataextractor 67 to the output terminal 69. The tape is halted for a periodcorresponding to the speed of the slow replay, and then normal speedreplay is again conducted. During the period (t2 to t3) when the tape ishalted, the data extractor 67 outputs the intra-picture data #2 as theslow replay data.

Then, normal speed replay is again conducted, and the operation similarto that described is repeated. The slow replay is thus continued.

In still replay, as in the slow replay, intra-picture data in the bitstream from the main areas, separated from the replay data, at the dataseparation circuit 60 is detected by the syntax analyzer 65, and thecounter 66 generates a timing signal, and the data extractor 67 extractsand stores the intra-picture data. When the tape transport is halted,the data extractor 67 keeps outputting the intra-picture data extractedimmediate before, as the still replay data. In this way, the normalspeed replay and the halting are intermittently conducted, to store andoutput the intra-picture in the bit stream from the main areas, and useit as the image data for slow or still replay, and the data for slow andstill replays is ensured, and slow or still replay images of a goodquality are obtained.

Embodiment 5

Embodiment 5 is for providing a digital VTR which is less easilyaffected by data errors due to recording and replay, and with which fastreplay at an arbitrary speed.

FIG. 17 is a block diagram showing a recording system of a digital VTRof Embodiment 5 of the invention. In the drawing, reference numeral 1denotes an input terminal for a bit stream with a packet length of 188bytes, 102 denotes a data identifying circuit, 103 denotes a dataextracting circuit, 104 denotes a variable-length decoder for compresseddata, 105 denotes a coefficient counter counting the number ofcoefficients created as a result of the decoding, 106 denotes a dataamount control circuit, 107 denotes an EOB (end of block) appendingcircuit, 108 denotes a buffer, 109 denotes an address control circuit,110 denotes a track format circuit, 111 denotes a header appendingcircuit, 112 denotes a recording signal processing circuit, and 113denotes an output terminal for a recording signal for a magnetic tape.

When recording onto a magnetic tape is conducted, transparent recordingis conducted, and at the same time, fast replay data is extracted andrecorded. The data identifying circuit 102 decodes the headerinformation of the bit stream input via the input terminal 1, andselects the transport packet containing the image of the intra-picturedata. The data extraction circuit 103 extracts intra-picture data withinthe transport packet, from the bit stream, and outputs the the encodeddata of the image block to the variable-length decoder 104. Thevariable-length decoder 104 having received the encoded code, outputsthe orthogonal transform coefficients of the image block, to thecoefficient counter 105. The coefficient counter 105 outputs the countvalue of the number of the orthogonal transform coefficients to the dataamount control circuit 106. The data amount control circuit 106 receivesthe coefficient count value and the amount of decoded data, and controlsthe data extraction circuit 103 so that the extracted data isaccommodated in one sync block under the condition that the sum of thecount values of the orthogonal transform coefficients is within apredetermined range.

The buffer 108 temporarily stores the bit stream and the fast replaydata output from the EOB appending circuit 107. In doing so, it readsthe data in the order in which it is recorded on the tape, under thecontrol by the address control circuit 109. The data output from thebuffer 108 is input to the track format circuit 110, where sync data, IDdata, parities are added for each sync block, and the header output fromthe header appending circuit 111 is appended to the data input from thebuffer 108, and the data is then output to the recording signalprocessing circuit 112, and then to the output terminal 113, as therecording signal to be recorded on the tape.

FIG. 18A and FIG. 18B are diagrams for explaining the decoding of theimage block in the recording system. FIG. 18A shows the configuration ofthe encoded data and the decoded data of the image block. In thedrawing, reference numeral 115 denotes an i-th image block data, and itslength is LBi (bits). Reference numeral 116 denotes orthogonalcoefficients obtained by decoding the encoded data (1, 2, . . . ) of theimage block data 115. FIG. 18B shows the configuration of the HP datafor fast replay. In the drawing, reference numeral 117 denotes dataextracted from the image block data 115, and its length is Xi (bits).

FIG. 19 is a flow chart showing the procedure of decoding the imageblock in the recording system. The method for determining the amount ofextracted data at the data amount control circuit 106 will next bedescribed with reference to FIG. 18A, FIG. 18B and FIG. 19. Thereference marks used in FIG. 18A, FIG. 18B and FIG. 19 in connectionwith the image block data are as follows:

-   -   i: image block number    -   LBi: data length (number of bits) of the i-th image block data        115    -   Xi: data length (number of bits) of the HP data extracted from        the i-th image block    -   j: number of the encoded code forming an image block    -   Lj: length (number of bits) of the J-th encoded code    -   Cj: number of orthogonal transform coefficients obtained by        decoding the j-th encoded code    -   L_(EOB): length (number of bits) of the EOB code    -   TM: control target of data amount (number of bits) for recording        in the sync block    -   D: permissible maximum value (number of bits) of vacant capacity    -   d: vacant capacity (number of bits)    -   S: sum of the numbers Cj of the j-th orthogonal transform        coefficient    -   CL: contact not smaller than 2    -   CH: constant larger than CL

Referring to FIG. 19, when the fast replay data is newly extracted, thecontrol data is initialized so that the number i of the image block isset to 1, and the vacant capacity d is set to TM (step a1—hereinaftersimply referred to as a1), and the data 115 of the i-th image block isread (a2). The length of the entire image block data 115 is LBi bits,and the length of the encoded code j which is a constituent thereof isLj bits, and an EOB code of a length of L_(EOB) is present at the end ofthe encoded code.

In the image block data 115, the encoded codes for the low-frequencycoefficients appear first. The value j is initialized to “1” (a3) andthen the encoded codes are decoded by the variable-length decoder 104(a4) to obtain Cj orthogonal transform coefficients (a5). The number Cjof the orthogonal transform coefficients varies with the encoded code j.The values Cj obtained by counting by the coefficient counter 105 areaccumulated, and the resultant sum S of the numbers Cj of the orthogonaltransform coefficients, up to the j-th encoded code is determined (a6).The accumulated value S is compared with a predetermined value CL (a7).If S is greater than CL, it is then compared with another constant CHgreater than CL (a8).

When the accumulated value S is smaller than CL, judgement is madewhether the length of the code including the encoded codes having beendecoded, with the EOB appended, is not longer than the vacant capacity d(a9). If it is not longer, j is incremented by one (a13), and theoperation returns to the step a4. When the accumulated value S is notsmaller than CL and not larger than CH, judgement is made whether thelength of the code including the encoded codes having been decoded, withthe EOB appended, is not longer than the vacant capacity d (a10). If itis not longer, the VLC codes (variable length codes) up to the j-th codeare extracted (a11). If the accumulated value S is judged to be largerthan CH at the step a8, and or if the code length is judged to exceedthe vacant capacity d, the VLC codes up to the (j-1)-th code areextracted (a12).

An EOB code is appended at the EOB appending circuit 107, to the codes117 that have thus been extracted (a14), and the sum Xi of the length ofthe j or (j-1) data having been extracted and the EOB code is determined(a15).

The sum (Σ Xi) of the length Xi of the data having been extracted issubtracted from the data amount target TM to find the vacant capacity d(a16), and judgement is made whether d is not larger than a permissiblevalue D (a17). If the vacant capacity d is larger than the permissiblevalue D, i is incremented by one (a19), and the operation returns to thestep a2, and the next image block is read. If d is not larger than thepermissible value D at the step a17, the data up to the image block i isoutput as the fast replay data to the buffer 108 (a18).

FIG. 20 shows the recording pattern of the fast replay data. In thedrawing, reference numeral 141 denotes the data region of 77 byte long,156 denotes a header of one byte appended at the header appendingcircuit 111, and i and (i+1) denote data of the image blocks for highspeed replay read from the buffer 108. Recorded in the header 156 isidentification information for intra-frame and the image blocks obtainedby extracting the fast replay data. The data of each image block isrecorded, without being divided into a plurality of sync blocks. Theconstant TM is dependent on the length of which can be data recorded inthe sync block, and CL and CM define the upper and lower limits for thenumber of the transform coefficients of the image used for the fastreplay. By the above procedure, the encoded data corresponding to theorthogonal transform coefficients of the length which is not smallerthan CL and not larger than CM is extracted from the bit stream, andused as the fast replay data. The fast replay data is recorded in thedata regions of one sync block on the magnetic tape, without the data ofthe image block being divided, with the vacant capacity being not largerthan D.

In the transparent recording, two packets of 188 byte long in the bitstream are recorded in five sync blocks on the tape. Each packet is readby the buffer 108, and then read by the address control circuit 109, anddivided into three, by selection of a bit, and according to thepredetermined bit position. The data of two packets, having beendivided, is input to the track format circuit 110, and a headergenerated by the header appending circuit 111 is appended, and therecording data of five consecutive sync blocks is reconstructed.

FIG. 21 shows a recording pattern of the packet. It illustrates, intwo-dimensional representation, the data of five sync blocks consecutiveon the tape region in which transparent recording is made. In thedrawing, reference numeral 141 denotes a data region of 77 bytes in onesync block, and the five rows respectively represent data of five syncblocks. Reference numerals 142 to 144 denote data of the first packetread from the buffer 108. Reference numerals 145 to 147 denote data ofthe second packet read from the buffer 108. Reference numerals 148 to152 denote first headers, each one byte long, appended at the headerappending circuit 111. Reference numerals 153 and 154 denote secondheaders, each two bytes long, appended at the header appending circuit111.

Regions 142 to 144 are respectively 74 bytes, 76 bytes and 38 byteslong, and the first packet is expressed by 188 bytes in total. Regions145 to 147 are respectively 36 bytes, 76 bytes and 76 bytes long, andthe second packet is expressed by 188 bytes in total.

The regions 148 to 152 are headers, and contain a flag indicatingwhether the corresponding sync block is a region for transparentrecording or a recording region for fast replay data, a flag foridentifying which of the five consecutive sync blocks, and a code forindicating the partition for of the first encoded data of the succeedingpacket data.

The regions 153 and 154 contain codes for indicating the type of thedata of the packet, e.g., video data, audio data, character data andprogram data.

FIG. 22 shows the recording track on the magnetic tape. In the drawing,reference numeral 160 denotes a track, 158 denotes a video recordingregion, 161 denotes a transparent recording region, and 162 denotes fastreplay data recording region. The numerical values along the trackrepresent the sync block numbers for the video regions. The region 161consists of five sync blocks consecutive to each other, and records thebit stream data shown in FIG. 21. The region 162 is one sync blockadjacent to the region 162, and records the fast replay data in theformat shown in FIG. 20. The regions 161 and 162 are disposedalternately in the video recording region 158.

FIG. 23 is a block diagram showing a replay system of a digital VTR ofEmbodiment 5. In the drawing, reference numeral 121 denotes a replaysignal input terminal, 122 is a data separation circuit for separatingthe transparent recording data and fast replay data from each other, 123denotes a buffer for forming a bit stream, 124 denotes a synthesizingcircuit for fast replay data, 125 denotes a bit stream forming circuitfor fast replay data, 126 denotes a fast replay speed selecting circuit,and 127 is an output terminal for the bit stream.

The signal replayed from the magnetic tape is input via the inputterminal 121 to the data separation circuit 122, and is separated intothe transparent recording data and the fast replay data. The transparentrecording data is read at a predetermined rate, in a sequence by thebuffer 123, and the data of a plurality of packets which were recorded,being divided, are read in sequence at a predetermined rate, so that abit stream identical to those is output via the output terminal 127.

When fast replay is to be conducted, the speed selection circuit 126controls the entire system so that the tape transport speed is at aneven-multiple speed, and the fast replay data synthesizing circuit 124collects the fast replay data without duplication, on the basis of thesignals replayed by the head. When the fast replay data is replayed, thedata of the intra frame is constructed and output to the bit streamforming circuit 125. The bit stream forming circuit 125 repeats theintra-frame data for a predetermined number of times, on the basis ofthe speed data from the speed selection circuit 126, and adds a packetheader to it, to form bit stream data. The bit stream data that has beenformed is output to the buffer 123, and is output from the buffer 123 ata predetermined rate.

Factors affecting the scanning pattern of the head at the time of thefast replay include the number and disposition of the heads on the drum,the width of each head, the angle over which the tape is wrapped aroundthe drum, and the tape transport speed. Head scanning patterns on theassumption that two head of different azimuths are disposed on the drum180° apart, and the angle over which the tape is wrapped around the drumis 180° will next be shown.

FIG. 24 shows the track format and head scanning pattern when the tapeis double-speed replayed. In the drawing, the character (“A” or “B”)written in each track 160 indicates whether the head used for recordingthe track is head A or head B. Reference numeral 171 denotes thescanning regions by a first head A, and reference numeral 172 denotesthe scanning region by a second head B. Reference numeral 173 denotestape region where data can be replayed by the first head A, andreference numeral 174 denotes tape region where data can be replayed bythe second head B. The width of the head is assumed to be identical tothe width of the track, and the tracks which are actually inclined areshown to be perpendicular to the longitudinal direction of the tape, forthe sake of simplicity of illustration.

The data recorded in the regions 173 and 174 can be picked up, but asthe overlapping between the track and the head becomes small, the signallevel become insufficient, so that the data cannot be reproduced.Usually, when the head and track overlaps more than half the trackwidth, then the data can be replayed. Accordingly, data can be replayedfrom the part of the region 173 below the line 175 and the part of theregion 174 above the line 175.

In the double-speed replay, if fast replay data is repeatedly recordedover four consecutive tracks as indicated by 176, all the data can bereplayed if scanned twice by the heads A and B. However, identical dataneed to be recorded in identical sync blocks of the four tracks.

The number of times the fast replay data is repeatedly recorded can bedetermined from the specification for the fast replay speeds of thedevice, and is set to be twice the multiplier of the maximum fast replayspeed.

FIG. 25 shows the track pattern and the head scanning pattern when therecorded tape is four-time speed replayed. In the drawing, the referencenumerals identical to those in FIG. 24 denote identical elements. Lines181 and 183 show the head scanning regions if the head width is 1.5times the track width. As described above, for four-time speed replay,fast replay data must be repeatedly recorded at least (4×2) or 8 times,to enable replay of all the data. However, in actual fast replay, thetape is transported at a high speed, so that the contact between thehead and the tape is unstable, and the level of the replay signal mayfluctuate. Moreover, as the tape transport speed varies a little, thehead scanning pattern may shifts from that illustrated. The regions 173and 174 may not cover all the data. In such a case, by using a head of awidth W2 (=W1×1.5, W1 representing the width the track), data in theregions 183 and 184 can also replayed, and all the fast replay data canbe replayed. This is next explained further.

FIG. 26A shows the signal level when the head of a width W1 is used forreplay from a track pattern shown in FIG. 25, and the track regions fromwhich data replay is possible. In the drawing, the horizontal axisrepresents the position in the longitudinal direction of the track, andthe vertical axis represents the replay signal level. 191 represents thereplay signal level by the head A, 192 represents the replay signallevel by the head B, 193 represents the half peak value, 194 denotes therecording region from which the fast replay data repeatedly recorded canbe replayed by the head A, and 195 denotes the recording regions fromwhich the data can be replayed by the head B.

By adding the regions 194 and 195, all the fast replay data recordedalong the entire length of the tracks can be replayed. However, when thereplay signal level varies, the data in the peripheries of the regions194 and 195 may not be replayed, and when the tape transport speedfluctuates, the regions 194 and 196 may shift left or right, forexample. In these cases, all the fast replay data cannot be replayedfrom the addition of the regions 194 and 195.

FIG. 26B shows the signal level when the head of a width W2 is used forreplay from the track pattern shown in FIG. 25, and the track regionsfrom which data replay is possible. When compared with FIG. 26A, thesignal levels 191 and 192 are increased by the amount corresponding tothe regions 183 and 184. As a result, the fast replay data of all thetrack are replayed sufficiently from the addition of the regions 194 and195 from which replay is possible.

In Embodiment 5, description is made for the case where the track formatis as shown in FIG. 22. However, the fast replay data may beconcentrated in a specific part of a track, for instance in the centralpart of the track. In this case, the parts of the track near the tapeedges where the signal level fluctuation is larger are not used, so thatthe fast replay data can be replayed stably.

The fast replay data may be concentrated at the beginning ends. In thiscase, it is possible to reduce the angle over which the tape is wrappedaround the drum, to thereby reduce the load on the tape transportsystem. In this way, the tape transport can be thereby stabilized, andthe speed for the fast replay can be increased.

In Embodiment 5, the fast replay data is repeatedly recorded for anumber twice the multiplier of the maximum fast replay speed. By addinga head C for use in fast replay only, having the same azimuth as thehead B, and being disposed near the head A, the fast replay datarecorded by the head B can be replayed simultaneously with the scanningby the head A. In this case, the speed of the fast replay can beincreased to double the multiplier of the above-mentioned maximum fastreplay speed.

In Embodiment 5, the fast replay data is recorded each sync block bysync block, but may alternatively be recorded, taking every two syncblocks as a unit. In this case, the constant TM is set to 76bytes×2×8=1216 bits.

Embodiment 6

FIG. 27 is a block diagram showing a recording system of a digital VTRof Embodiment 6 of the invention. In the drawings, reference numeral 1denotes an input terminal for receiving the digital video signal in theform of a bit stream, 202 denotes a packet detecting circuit fordetecting packets of the video signal from the bit stream having beensupplied, 203 denotes a first memory for storing the data from thepacket detecting circuit 202, packet by packet, 204 denotes an intradetecting circuit for detecting whether the transport packet contains anintra-picture data, 205 denotes a fast replay data generating circuitreceiving the transport packet containing intra-picture data and formingfast replay data, and 206 denotes a second memory for storing the fastreplay data formed by the fast replay data generating circuit 205.Reference numeral 207 denotes a first first header appending circuit forappending a header to the data read from the first memory 203. Referencenumeral 208 denotes a second header appending circuit for appending aheader to the data read from the second memory 206. Reference numeral209 denotes a format circuit for forming video areas from the inputdata, 210 denotes a error correction encoder for performing errorcorrection encoding, 211 denotes digital modulator for conversion intodata suitable for recording on the tape, 212 denotes a recordingamplifier, 213 denotes a rotary drum, and 214 a and 214 b denotemagnetic heads.

FIG. 28 shows data format of the video areas in the digital VTR.

FIG. 29 to FIG. 31 show data packets according to this embodiment. FIG.29 shows the configuration of the transport data packet contained in theinput bit stream. FIG. 30 shows the configuration of data of the mainarea recorded on the magnetic tape. FIG. 31 shows the configuration ofdata in the copy area.

The operation in the recording in the digital VTR of Embodiment 6 willnext be described with reference to FIG. 27 to FIG. 31. The bit streaminput via the input terminal 1 contains digital video and audio signals,and digital data signals concerning the video and audio signals, andthey are transmitted, being partitioned into transport packets, as shownin FIG. 29. Each transport packet comprises a header of 4 bytes, and adata section of 184 bytes.

In the present digital VTR, low-frequency components are extracted fromthe transport packets containing intra-picture data to form fast replaydata, or so-called HP data, and the transport packets are recorded inthe main areas and the fast replay data is recorded in the copy areas.The input bit stream is supplied to the packet detecting circuit 202where the transport packets are detected, and sent to the first memory203 and the intra detecting circuit 204.

The first memory 203 stores the bit stream data packet by packet, andthe data is read so that it forms recording data packet shown in FIG.30. FIG. 30 shows the case where the length of data within one syncblock is 77 bytes, and two transport packets are used to form five syncblocks. In the drawing, H1 denotes a first header, and H2 denotes asecond header. H1 is positioned at the head of each sync block, andcontains a flag indicating whether the sync block belongs to the mainareas or to the copy areas. H2 is positioned at the head of eachtransport packet, and contains a flag indicating the transport packetsucceeding the H2 header contains an intra-picture data.

The transport packet data read from the first memory 203 is input to thefirst header appending circuit 207, where H1 and H2 headers areappended, and made into a packet configuration shown in FIG. 30, and isthen supplied to the format circuit 209.

The intra detecting circuit 204 finds whether the data in the transportpacket contains data of intra-picture data. The fast replay datagenerating circuit 205 extracts low-frequency component from the packetcontaining the detected intra-picture data, to generate HP data, andsupplies it to the second memory 206.

The second memory 206 stores HP data sent from the fast replay datagenerating circuit 205, and the data is read so that the recording dataconfiguration is as shown in FIG. 31. In the drawing, H1 denotes a firstheader identical to that in FIG. 30. The fast replay data read from thesecond memory is supplied to the second header appending circuit 208,where H1 header is appended, and is formed into the configuration shownin FIG. 31, and sent to the format circuit 209.

The format circuit 209 combines the data from the main areas output fromthe header appending circuit 207, and the data from the copy areasoutput from the second header appending circuit 208 to form data of onetrack, and sends it to the error correction encoder 210, where errorcorrection encoding is performed on input data of one track. The outputof the error correction encoder 210 is digital-modulated at the digitalmodulator 211 into data format suitable for recording on the tape, andpassed through the recording amplifier 212, and recorded on the magnetictape by means of the rotary heads 214 a and 214 b.

The operation for normal replay will next be described.

FIG. 32 is a block diagram showing a replay system of a digital VTR ofEmbodiment 6. In the drawing, reference numerals 213, 214 a and 214 bdenote members identical to those in FIG. 27. Reference numeral 215denotes a replay amplifier, 216 denotes a digital demodulator, 217denotes a sync header detecting circuit, 218 denotes a third memory, 219denotes an error correction decoder for correction replay errors, 220denotes a data separation circuit for separating the data by checking H1header in each sync block, and selectively outputting data according tothe replay mode, 221 denotes an intra detection circuit for checking H2header in the data output from the data separation circuit 220, andfinding transport packets containing an intra-picture data, 222 denotesa data extractor for extracting transport packets containing anintra-picture data, and 223 denotes a fourth memory for extracting forstoring the data extracted by the data extractor 222. Reference numeral224 denotes a selector for selectively outputting the data according tothe replay mode, and 225 denotes an output terminal for outputting thedata selected by the selector 224.

In normal replay, the data replayed by the magnetic heads 214 a and 214b from the magnetic tape is amplified by the replay amplifier 215, andis input to the digital demodulator 216. The digital demodulator 216performs digital demodulation on the input data, and outputs thedemodulated data to the sync header check circuit 217. The sync headercheck circuit 217 checks sync headers in the demodulated sync blocks,and stores the data in the third memory 218, according to the headerinformation that has been read. Any replay errors in the data recordedin the third memory 218 are corrected, and the error-corrected data isoutput to the data separation circuit 220.

The data separation circuit 220 checks the H1 headers in the data readfrom the third memory 218, and separates it into normal replay transportpackets, and fast replay data, and outputs the normal replay transportpackets to the selector 224, and outputs the H2 headers having beenappended to the head of the transport packet to the intra detectioncircuit 221. At this stage, the H1 and H2 headers are removed from thetransport packets.

The intra detection circuit 221 reads the H2 header output from the dataseparation circuit 222, and checks whether the transport packet to whichthe H2 header has been appended contains an intra-picture data. If anintra-picture data is contained, the intra detection circuit 221 sends acontrol signal for causing the the data extractor 222 to extracts thepacket. In accordance with the control signal from the intra detectioncircuit 221, the data extractor 222 extracts the transport packet, andoutputs it to the fourth memory 223. As a result, the transport packetsextracted by the data extractor 222 are sequentially stored in thefourth memory 223.

The selector 224 selectively outputs the output of the data separationcircuit 220, or the output of the fourth memory 223, to the outputterminal 225. In normal replay, the output from the data separationcircuit 220 is selected, and output via the output terminal 225.

Next, let us consider a situation case where a still replay mode isselected during normal replay. In normal replay, the data replayed bythe magnetic heads 214 a and 214 b from the magnetic tape is amplifiedby the replay amplifier 215, and is then input to the digitaldemodulator 216. The digital demodulator 216 performs digitaldemodulation on the input data, and outputs the demodulated data to thesync header check circuit 217. The sync header check circuit 217 checksthe sync header in the demodulated sync block, and stores the data inthe third memory 218 according to the header information that has beenread. Any replay errors contained in the data recorded in the thirdmemory 218 are corrected at the error correction decoder 219. and theerror-corrected data is output to the data separation circuit 220.

The data separation circuit 220 checks the H1 headers in the data readfrom the third memory 218, and separates it into normal replay transportpackets, and fast replay data, and outputs the normal replay transportpackets to the selector 224, and outputs the H2 headers having beenappended to the head of the transport packet to the intra detectioncircuit 221.

The intra detection circuit 221 reads the H2 header output from the dataseparation circuit 222, and checks whether the transport packet to whichthe H2 header has been appended contains an intra-picture data. If anintra-picture data is contained, the intra detection circuit 221 sends acontrol signal for causing the the data extractor 222 to extracts thepacket. In accordance with the control signal from the intra detectioncircuit 221, the data extractor 222 extracts the transport packet, andoutputs it to the fourth memory 223. As a result, the transport packetsextracted by the data extractor 222 are sequentially stored in thefourth memory 223.

The selector 224 selectively outputs the output of the data separationcircuit 220, or the output of the fourth memory 223, to the outputterminal 225. In normal replay, the output from the data separationcircuit 220 is selected, and output via the output terminal 225.

When still replay is selected during normal replay, the output of thetransport packets for normal replay is stopped, and the output of thedata from the selector to the output terminal 225 is terminated. Theinput to the selector 224 is switched, and the output of the fourthmemory 223 is selected, so that still picture can be output via theoutput terminal 225.

Slow replay will next be described. During slow replay, the magnetictape transport speed is lower than in normal replay, and the magnetictape is transported while the same helical track is scanned and replayeda plurality of times. In particular, when the tape speed is ½multiple-speed or less, the same track is replayed at least twice, sothat it is possible to replay all the data of one track through thechecking of the sync header at the sync header check circuit 217, andthe error correction at the error correction decoder 219. The replayeddata is recorded in the third memory 218.

The data separation circuit 220 checks the H1 headers in the data readfrom the third memory 218, and separates it into normal replay transportpackets, and fast replay data, and outputs the normal replay transportpackets to the selector 224, and outputs the H2 headers having beenappended to the head of the transport packet to the intra detectioncircuit 221.

The intra detection circuit 221 reads the H2 header output from the dataseparation circuit 222, and checks whether the transport packet to whichthe H2 header has been appended contains an intra-picture data. If anintra-picture data is contained, the intra detection circuit 221 sends acontrol signal for causing the the data extractor 222 to extracts thepacket. In accordance with the control signal from the intra detectioncircuit 221, the data extractor 222 extracts the transport packet fornormal replay, and outputs it to the fourth memory 223. As a result, thetransport packets extracted by the data extractor 222 are sequentiallystored in the fourth memory 223. The selector 224 selectively outputsthe output of the data separation circuit 220, or the output of thefourth memory 223, to the output terminal 225. In slow replay, theoutput from the data separation circuit 220 is selected, and output viathe output terminal 225.

The operation in fast replay will next be described. In fast replay, thedata replayed by the magnetic heads 214 a and 214 b from the magnetictape is amplified by the replay amplifier 215, and is then input to thedigital demodulator 216. The digital demodulator 216 performs digitaldemodulation on the input data, and outputs the demodulated data to thesync header check circuit 217. The sync header check circuit 217 checksthe sync header in the demodulated sync block, and stores the data inthe third memory 218 according to the header information that has beenread. Any replay errors contained in the data recorded in the thirdmemory 218 are corrected at the error correction decoder 219. and theerror-corrected data is output to the data separation circuit 220.

The data separation circuit 220 checks the H1 headers in the data readfrom the third memory 218, and separates it into normal replay transportpackets, and fast replay data, and outputs only the fast replay data tothe selector 224.

The selector 224 selectively outputs the output of the data separationcircuit 220, or the output of the fourth memory 223, to the outputterminal 225. In fast replay, the output from the data separationcircuit 220 is selected, and output via the output terminal 225.

Embodiment 7

FIG. 33 is a block diagram showing a recording system of a digital VTRof Embodiment 7 of the invention. In the drawing, reference numeral 1denotes an input terminal for receiving an input bit stream, 4 denotes avariable-length decoder for analyzing the header in the input bitstream, and detecting the intra-encoded block to perform variable-lengthdecoding, 5 denotes a counter for counting the number of blocks formingthe variable-length decoded intra-picture data, 6 denotes a dataextraction circuit for extracting HP data for fast replay, from theinput bit stream, in accordance with instructions from the counter, 7denotes an EOB appending circuit for appending EOB codes to the HP datahaving been extracted, and 258 denotes an HP data output terminal.Reference numeral 260 denotes an HP data format circuit for formattingthe HP data according to a designated pattern, 261 denotes a trackcounter for counting the track numbers, and 262 denotes a patterngenerating circuit for determining the position at which the HP data isto be recorded, for each track, on the basis of the count value at thetrack counter 261. Reference numeral 263 denotes a phase signalgenerating circuit for generating a phase signal having a valueidentical throughout each track group, according to the input from thetrack counter 261. Reference numeral 264 denotes a recording data formatcircuit 264.

The operation will next be described. The operation from the inputterminal 1 to the EOB appending circuit 7 is identical to that of theprior art example of FIG. 43. The HP data output from the EOB appendingcircuit 7 is input to the HP data format circuit 260, where the input HPdata is stored in a memory within the HP data format circuit 260. Thetrack counter 261 keeps counting the number of tracks until therecording of HP data in a designated track group is completed. Each timerecording of different HP data in the tracks is started, the count valueis reset. The count value generated from the track counter 261 issupplied to the pattern generating circuit 262 and the phase signalgenerator 263. The pattern signal from the pattern signal generator 262is supplied to the HP data format circuit 260 and the recording dataformat circuit 264, and the phase signal from the phase signalgenerating circuit 263 is supplied to the recording data format circuit264.

FIG. 34 shows the recording pattern of the HP data recorded in thetracks. It is assumed that “17” is the multiplier of the maximum fastreplay speed, as in the prior art example. As in the prior art example,two heads are disposed opposite to each other, 180° apart from eachother, and the tape is wrapped around the drum over 180°.

“A”, “B” and “C” indicate, by the same alphabetic character, identicalHP data is recorded over 17 tracks. The numerals succeeding thealphabetic characters denotes different HP data are recorded indifferent track groups, each consisting of 17 tracks. The combinationsof the alphabetic characters and numerals indicate, as in FIG. 44, thatthey are identical data.

More specifically, the recording patterns of the tracks forming onetrack group consisting of 17 tracks include

-   -   a pattern TP1 in which HP data B is recorded in the copy area at        the center of the track, and HP data A is recorded in the copy        areas at both ends of the track,    -   a pattern TP2 in which HP data A is recorded in the copy area at        the center of the track, and HP data C is recorded in the copy        areas at both ends of the track,    -   a pattern TP3 in which HP data A is recorded in the copy areas        at the center and both ends of the track,    -   a pattern TP4 in which HP data C is recorded in the copy area at        the center of the track, and HP data A is recorded in the copy        areas at both ends of the track,    -   a pattern TP5 in which HP data B is recorded in the copy area at        the center of the track, and HP data C is recorded in the copy        areas at both ends of the track, and    -   a pattern TP6 in which HP data B is recorded in the copy areas        at the center and both ends of the track, and    -   in one track group,    -   a first track of pattern TP4 is disposed in the center of the        track group,    -   a second track of pattern TP1 is disposed at one end (at the        head, in the illustrated example) of the track group,    -   a third track of pattern TP6 is disposed at the opposite end (at        the tail, in the illustrated example) of the track group,    -   tracks of patterns TP2 and TP3 are alternately and repeatedly        disposed between the first track and the second track,    -   tracks of patterns TP5 and TP6 are alternately and repeatedly        disposed between the first track and the third track.

The count value of the track counter 261 varies from “0” to “16” andthis enables identification of each of the 17 tracks in each trackgroup. The count value of the track counter 261 is reset every 17tracks. The track counter 261 generates such a count value, and outputsit to the pattern generating circuit 262 and the phase signal generator263.

FIG. 35 shows the pattern signal generated by the pattern generatingcircuit. The track counter 261 is reset at the head of 17 tracks, andits count value is incremented by one every track, and its count valueis output to the pattern generating circuit 262. On the basis of thevalue input from the track counter 261, the pattern generating circuit262 outputs a pattern signal, as a signal for specifying HP data to berecorded in the particular track. For instance, when a pattern shown inFIG. 34 is to be generated, at the first track in the group of tracksconsisting of 17 tracks, the value of the track counter 261 is “0”, andthe pattern generating circuit 262 outputs a pattern ABA (FIG. 35)corresponding to the counter value “0”. The pattern generating circuit262 has a arrangement map for HP data for 17 tracks shown in FIG. 35,and specifies one of the pattern signals from the arrangement table,depending on the value of the track counter 261 input to the patterngenerating circuit 262. According to the pattern signal generated by thepattern generating circuit 262, the HP data format circuit 260 outputsthe HP data in the order of A, and B and again A. The pattern signalfrom the pattern generating circuit 262 is also sent to the recordingformat circuit 264.

The track counter 261 also outputs the counter value to the phase signalgenerator 263. The phase signal generator 263 generates a phase whosevalue varies every 17 tracks and maintained constant for the period of17 tracks. The value of the phase signal varies every 17 track period,and within each track group formatted with an identical phase signal,the 17 track and next 17 tracks or immediately preceding 17 tracks canbe discriminated. The phase signal is also input to the recording dataformat circuit 264. The phase signal generator 263 receives the inputfrom the track counter 261, and varies its value. As long as it ispossible to discriminate between the group of 17 tracks to which theparticular track belongs, and the group of 17 tracks which are crossedduring fast replay, any other signal may be used. If for instance, themultiplier of the fast replay speed is 17, two groups of 17 tracks arecrossed, and it is sufficient if the two groups of the 17 tracks arediscriminated from each other. The phase signal generator 263 maytherefore generates a one-bit signal of “0” and “1”, alternately.

FIG. 36 shows the data configuration of the track. FIG. 37 shows thedata configuration of the sync block. The recording data format circuit264 forms data of a track as shown in FIG. 36. The sync block numbersallotted to the video area are from No. 0 to No. 134. At three locationsin the video area, HP data areas are provided, and the HP data outputfrom the HP data format circuit 260, together with the pattern signalfrom the pattern generating circuit 262 and the phase signal from thephase signal generator 263, are output via the output terminal 258. Asshown in FIG. 37, the sync blocks are one of the two types, i.e., afirst type of sync blocks 265 in the main areas, in which ATV bitstream, and parities are recorded, after SYNC and ID, and a second typeof sync blocks 266 in the copy areas, in which, after SYNC and ID, thephase signal (PHASE) from the phase signal generator 263, the HP datanumber which can be identified by the signal from the pattern generatingcircuit 262, and then the HP data and parities are recorded. These syncblocks form part of the data of the track. In addition to these data,sync blocks in the AUX data area as defined for the VTR of the SDspecification, form the data of the track. In this way, the data on thetape shown in FIG. 34 is formed. With the data thus formed, the fastreplay can be conducted with any of a number of differentmultiple-speeds. For instance, +3-time fast replay cannot be achievedwith the arrangement of data of the prior art example shown in FIG. 44.This is because, the HP data recorded in the center of the tracks on thetape that is scanned, and the HP data at both ends of the tracks arealways of different azimuths.

If however, the HP data is arranged as in Embodiment 7, while the 17tracks with an identical phase signal are scanned by the head, at leastone set each of A, B and C HP data can be obtained. It is possible todetect whether the data is HP data or not, from the sync block numbercontained in the ID, and when the data is found to be HP data, thendiscrimination is made to find which of the A, B and C HP data, thedetected HP data with an identical phase signal is, and while the headscans the 17 tracks, at least one set each of the A, B and C HP data canbe obtained.

In Embodiment 7, one track groups consists of 17 tracks. But theinvention is not limited to such configuration of the track group, andeach track group may consists of tracks the number of which is given by:6×m+5, or4×n+5,where m and n are integers not smaller than “1”, and satisfying 3×m=2×n.According, it is sufficient if I track groups (I being a positiveinteger) are formed of J tracks where J=12×I+5.

In Embodiment 7, it is assumed that all the intra-picture data containedin the input bit stream are used. Detection of the intra-picture datacan be facilitated if only those intra-picture data which are containedin the intra-frame or intra-field the are used. This is because whenvariable-length decoding is effected the header of the input bit streamis detected, and the intra-picture data is recognized from the header.When the intra-picture data used as the HP data is limited tointra-frame or intra-field, it is not necessary to detect the intrainformation attendant to the macro block, and the picture headerattendant to the head of one frame can be utilized to simplify thedetection of intra-picture data.

Embodiment 8

FIG. 38 shows a recording pattern of HP data on tracks in Embodiment 8.

In Embodiment 7, the recording pattern shown in FIG. 34 is used. InEmbodiment 8, the recording patterns of the tracks forming one trackgroup include

-   -   a pattern TP1 in which HP data B is recorded in the copy area at        the center of the track, and HP data A is recorded in the copy        areas at both ends of the track,    -   a pattern TP2 in which HP data A is recorded in the copy area at        the center of the track, and HP data B is recorded in the copy        areas at both ends of the track,    -   a pattern TP3 in which HP data A is recorded in the copy areas        at the center and both ends of the track,    -   a pattern TP4 in which HP data A is recorded in the copy area at        the center of the track, and HP data C is recorded in the copy        areas at both ends of the track,    -   a pattern TP5 in which HP data C is recorded in the copy area at        the center of the track, and HP data A is recorded in the copy        areas at both ends of the track,    -   a pattern TP6 in which HP data C is recorded in the copy areas        at the center and both ends of the track,    -   a pattern TP7 in which HP data C is recorded in the copy area at        the center of the track, and HP data B is recorded in the copy        areas at both ends of the track,    -   a pattern TP8 in which HP data B is recorded in the copy area at        the center of the track, and HP data C is recorded in the copy        areas at both ends of the track, and    -   a pattern TP9 in which HP data B is recorded in the copy areas        at the center and both ends of the track, and    -   in one track group,    -   a first track of pattern TP5 is disposed in the center of the        track group,    -   second and third tracks of pattern TP6 are disposed on both        sides of and adjacent to the first track of pattern TP5,    -   a fourth track of pattern TP5 is disposed adjacent one of the        second and third tracks of pattern TP6,    -   a fifth track of pattern TP7 is disposed adjacent the other of        the second and third tracks, and on the opposite side of the        fourth track of pattern TP5, with respect to the first track,    -   a sixth track of pattern TP1 is disposed at the head or tail (at        the head in the illustrated example) of the track group, and on        the same side of the first track as the fourth track,    -   a seventh track of pattern TP2 is disposed next to the track of        pattern TP1, and on the same side of the first track as the        fourth track,    -   an eighth track of pattern TP9 is disposed at the tail or head        (at the tail, in the illustrated example) of the track group,        and on the same side of the first track as the fifth track,    -   tracks of patterns TP3 and TP4 are alternately and repeatedly        disposed between the seventh track and the fourth track,    -   tracks of patterns TP8 and TP9 are alternately and repeatedly        disposed between the eighth track and the fifth track.

In Embodiment 8, each track group consists of 17 tracks. The inventionis not limited to the particular number of the tracks, and may also beapplicable if the number of tracks forming a track groups is a tracknumber given by 6×m+5 or 4×n+5 where m and n are integers not smallerthan 1 and satisfying 3×m=2×n, that is the number of tracks forming atrack group may be J given by J=12×I+5, where I is a positive integer.

In Embodiment 8, the intra-picture data contained in the input bitstream are all used. But detection of intra-picture data is facilitatedif intra-picture data contained in intra-frame or intra-field.

This is because of the following reason. That is, when variable-lengthencoding is performed, the header of the input bit stream is detected,and the intra-picture data is recognized from the header. But if theintra-picture data used as the HP data is limited to intra-frame orintra-field, it is unnecessary to detect intra-information attendant tothe macro blocks and the detection of the intra-picture data can besimplified by utilizing the picture header attendant to the head of oneframe.

Embodiment 9

In connection with Embodiment 9, replay from the tape recorded inEmbodiment 7 and Embodiment 8 is explained. FIG. 39A and FIG. 39B showan example of replay system of a digital VTR of Embodiment 9. It isassumed, as in the prior art example, that the drum has two headsopposite to each other, and 180° apart from each other, and the tape iswrapped around the drum over 180°.

Reference numeral 270 denotes main areas in which the input bit streamis recorded on the tape, without modification, 271 denotes copy areas inwhich the low-frequency components of the DCT coefficients of theintra-picture data, extracted from the input bit stream, are recorded asHP data, 272 denotes a data separation circuit for selecting the outputreplay bit stream from the bit stream from the main areas and the bitstream from the copy areas, and 273 denotes a data reconstructioncircuit for combining, for reconstruction, the HP data output from thedata separation circuit during fast replay.

During normal replay, the data from the main areas 270 and the data fromthe copy areas 271 are input and Judgement is made whether the syncblock of the main area or the sync block of the copy areas is beingreplayed, in accordance with the ID in the sync block, and the data ofthe main areas is selected as the replay data.

During fast replay, the data separation circuit 272 outputs the syncblocks from the copy areas, in accordance with the ID's from therespective sync blocks. The data reconstruction circuit 273 checks thephase signal of the data of the input sync block, checks the HP datanumber in the sync blocks having identical phase signal, and forms a setof three HP data recorded in one track group. In this way, a bit streamof intra-picture data is formed, and is output to the decoder.

FIG. 40 is a diagram showing a scanning trace of the rotary head at thetime of seven-time speed replay. The operation of the seven-time speedreplay from the magnetic tape of the recording pattern of FIG. 34 willnext be described. One track group consists, for example of 17n tracks,as indicated by RP, at the bottom of the drawing, and A, B and C HP dataare recorded 17 times each. Let us consider a situation where first andsecond heads scan at a seven-time speed.

When the first head records tracks without hatching, and the second headrecords tracks with hatching. When the first head scans as shown on theleft side of the drawing only data A1 can be obtained as the HP databecause of the azimuth. The data A1 is stored in the data reconstructioncircuit 273. When the second head scans, only data C1 can be obtained.This data is also stored in the data reconstruction circuit 273. Thephase signal is then checked, and if it is identical to the phase signalof A1 earlier obtained, then the data C1 is stored together with A1. Ifthe phase signal is different, the data A1 is discarded, and only thedata C1 is stored. In this case, the HP data of the A1 and C1 arestored. Finally, the data B1 and C1 can be obtained when the first headscans the tape. The phase signal of the data B1 is identical to that ofA1 and C1, but the phase signal of the data C2 is different from that ofA1 and C1. When B1 is obtained, a set of A1, B1 and C1 is completed, andthe HP data is reconstructed. The C2 data is newly stored.

In this way, the bit stream from the main areas 270 can be replayedduring normal replay, and HP data is reconstructed during fast replay toreproduce bit stream of intra-picture data.

1. A playback device for replaying a bit stream digitally transmitted,comprising: detecting means for detecting intra-picture data in the bitstream that is replayed; extracting means for extracting theintra-picture data from the replayed bit stream, according to the resultof the detection at the detecting means; replay mode designating meansfor selecting and designating one of normal replay, slow replay andstill replay, as a replay mode; and replay data outputting means forstoring the extracted intra-picture data, and outputting theintra-picture data as the replay picture data, according to a modesignal output by said replay mode designating signal.
 2. A playbackdevice as set forth in claim 1, wherein said replay data output meanscomprises: address detecting means for detecting an address at which theintra picture data is recorded; control means for causing normal speedreplay and reversing, for reverse control, on the basis of the result ofthe detection of the address.
 3. A playback device as set forth in claim1, wherein said replay data output means comprises: control means forstopping the replay for a predetermined period after all theintra-picture data is extracted from the bit stream by normal speedreplay.